Methods of removing heat from an electrode using thermal shunting

ABSTRACT

According to some embodiments, a medical instrument (for example, an ablation device) comprises an elongate body having a proximal end and a distal end, an energy delivery member positioned at the distal end of the elongate body, a first plurality of temperature-measurement devices carried by or positioned within the energy delivery member, the first plurality of temperature-measurement devices being thermally insulated from the energy delivery member, and a second plurality of temperature-measurement devices positioned proximal to a proximal end of the energy delivery member, the second plurality of temperature-measurement devices being thermally insulated from the energy delivery member.

RELATED APPLICATIONS

This application is a continuation of U.S. patent application Ser. No.15/336,648 filed Oct. 27, 2016, which is a continuation of U.S. patentapplication Ser. No. 15/214,376 filed Jul. 19, 2016, which is acontinuation of PCT Application No. PCT/US2015/061419 filed Nov. 18,2015. PCT Application No. PCT/US2015/061419 claims priority to U.S.Provisional Application No. 62/081,710 filed Nov. 19, 2014, U.S.Provisional Application No. 62/094,892 filed Dec. 19, 2014, U.S.Provisional Application No. 62/135,046 filed Mar. 18, 2015, U.S.Provisional Application No. 62/135,025 filed Mar. 18, 2015, U.S.Provisional Application No. 62/211,539 filed Aug. 28, 2015, and U.S.Provisional Application No. 62/138,338 filed Mar. 25, 2015. The contentsof each of the above-referenced applications are incorporated herein byreference in their entireties.

BACKGROUND

Tissue ablation may be used to treat a variety of clinical disorders.For example, tissue ablation may be used to treat cardiac arrhythmias byat least partially destroying (e.g., at least partially or completelyablating, interrupting, inhibiting, terminating conduction of, otherwiseaffecting, etc.) aberrant pathways that would otherwise conduct abnormalelectrical signals to the heart muscle. Several ablation techniques havebeen developed, including cryoablation, microwave ablation, radiofrequency (RF) ablation, and high frequency ultrasound ablation. Forcardiac applications, such techniques are typically performed by aclinician who introduces a catheter having an ablative tip to theendocardium via the venous vasculature, positions the ablative tipadjacent to what the clinician believes to be an appropriate region ofthe endocardium based on tactile feedback, mapping electrocardiogram(ECG) signals, anatomy, and/or fluoroscopic imaging, actuates flow of anirrigant to cool the surface of the selected region, and then actuatesthe ablative tip for a period of time and at a power believed sufficientto destroy tissue in the selected region.

Successful electrophysiology procedures require precise knowledge aboutthe anatomic substrate. Additionally, ablation procedures may beevaluated within a short period of time after their completion. Cardiacablation catheters typically carry only regular mapping electrodes.Cardiac ablation catheters may incorporate high-resolution mappingelectrodes. Such high-resolution mapping electrodes provide moreaccurate and more detailed information about the anatomic substrate andabout the outcome of ablation procedures. High-resolution mappingelectrodes can allow the electrophysiology to evaluate precisely themorphology of electrograms, their amplitude and width and to determinechanges in pacing thresholds. Morphology, amplitude and pacing thresholdare accepted and reliable electrophysiology (EP) markers that provideuseful information about the outcome of ablation.

SUMMARY

According to some embodiments, a device for ablation and high-resolutionof cardiac tissue comprises an elongate body (e.g., catheter, othermedical instrument, etc.) comprising a distal end and an electrodeassembly positioned along the distal end of the elongate body, whereinthe electrode assembly comprises a first electrode portion, at least asecond electrode portion positioned adjacent the first electrodeportion, the first electrode portion and the second electrode portionbeing configured to contact tissue of a subject and deliverradiofrequency energy sufficient to at least partially ablate thetissue, at least one electrically insulating gap positioned between thefirst electrode portion and the second electrode portion, the at leastone electrically insulating gap comprising a gap width separating thefirst and second electrode portions, and at least one separatorpositioned within the at least one electrically insulating gap, whereinthe at least one separator contacts a proximal end of the firstelectrode portion and the distal end of the second electrode portion.The device additionally comprises at least one conductor configured toelectrically couple an energy delivery module to at least one of thefirst and second electrode portions, wherein the at least one conductoris electrically coupled to an energy delivery module and wherein afrequency of energy provided to the first and second electrodes is inthe radiofrequency range.

According to some embodiments, the device further comprises a filteringelement electrically coupling the first electrode portion to the secondelectrode portion and configured to present a low impedance at afrequency used for delivering ablative energy via the first and secondelectrode portions, wherein the filtering element comprises a capacitor,wherein the capacitor comprises a capacitance of 50 to 300 nF (e.g., 100nF, 50-100, 100-150, 150-200, 200-250, 250-300 nF, values between theforegoing ranges, etc.), wherein the elongate body comprises at leastone irrigation passage, said at least one irrigation passage extendingto the first electrode portion, wherein the first electrode portioncomprises at least one outlet port in fluid communication with the atleast one irrigation passage, wherein the gap width is approximately 0.2to 1.0 mm (e.g., 0.2, 0.2-0.3, 0.3-0.4, 0.4-0.5, 0.5-0.6, 0.6-0.7,0.7-0.8, 0.8-0.9, 0.9-1.0 mm, values between the foregoing ranges, lessthan 0.2 mm, greater than 1 mm, etc.), wherein a series impedance oflower than about 3 ohms (Ω) (e.g., e.g., 0-1, 1-2, 2-3 ohms, valuesbetween the foregoing ranges, etc.) is introduced across the first andsecond electrode portions in the operating RF frequency range, andwherein the operating RF frequency range is 200 kHz to 10 MHz (e.g.,200-300, 300-400, 400-500, 500-600, 600-700, 700-800, 800-900, 900-1000kHz, up to 10 MHz or higher frequencies between the foregoing ranges,etc.). Electrode portions or sections can be used interchangeably withelectrodes herein.

According to some embodiments, the device further comprises a firstplurality of temperature-measurement devices positioned within separateapertures formed in a distal end of the electrode assembly, the firstplurality of temperature-measurement devices (e.g., thermocouples, othertemperature sensors, etc.) being thermally insulated from the electrodeassembly, and a second plurality of temperature-measurement devices(e.g., thermocouples, other temperature sensors, etc.) positioned withinseparate apertures located in relation to the proximal end of theelectrode assembly, the second plurality of temperature-measurementdevices being thermally insulated from the electrode assembly, whereintemperature measurements determined from the first plurality oftemperature-measurement devices and the second plurality oftemperature-measurement devices facilitate determination of orientationof the electrode assembly with respect to tissue being treated, and atleast one thermal shunt member placing a heat absorption element inthermal communication with the electrode assembly to selectively removeheat from at least one of the electrode assembly and tissue beingtreated by the electrode assembly when the electrode assembly isactivated, a contact sensing subsystem comprising a signal sourceconfigured to deliver a range of frequencies to the electrode assembly,and a processing device configured to obtain impedance measurementswhile different frequencies within the range of frequencies are beingapplied to the electrode assembly by the signal source, process theimpedance measurements obtained at the different frequencies, anddetermine whether the electrode assembly is in contact with tissue basedon said processing of the impedance measurements, wherein the elongatebody comprises at least one irrigation passage, said at least oneirrigation passage extending to the first electrode portion.

According to some embodiments, the device further comprises a firstplurality of temperature-measurement devices (e.g., thermocouples, othertemperature sensors, etc.) positioned within separate apertures formedin a distal end of the electrode assembly, the first plurality oftemperature-measurement devices being thermally insulated from theelectrode assembly, and a second plurality of temperature-measurementdevices (e.g., thermocouples, other temperature sensors, etc.)positioned within separate apertures located in relation to the proximalend of the electrode assembly, the second plurality oftemperature-measurement devices being thermally insulated from theelectrode assembly, wherein temperature measurements determined from thefirst plurality of temperature-measurement devices and the secondplurality of temperature-measurement devices facilitate determination oforientation of the electrode assembly with respect to tissue beingtreated.

According to some embodiments, the device further comprises at least onethermal shunt member placing a heat absorption element in thermalcommunication with the electrode assembly to selectively remove heatfrom at least one of the electrode assembly and tissue being treated bythe electrode assembly when the electrode assembly is activated.

According to some embodiments, the device further comprises a contactsensing subsystem comprising a signal source configured to deliver arange of frequencies to the electrode assembly, and a processing deviceconfigured to obtain impedance measurements while different frequencieswithin the range of frequencies are being applied to the electrodeassembly by the signal source, process the impedance measurementsobtained at the different frequencies, and determine whether theelectrode assembly is in contact with tissue based on said processing ofthe impedance measurements.

According to some embodiments, the filtering element comprises acapacitor. In some embodiments, the capacitor comprises a capacitance of50 to 300 nF (e.g., 100 nF, 50-100, 100-150, 150-200, 200-250, 250-300nF, values between the foregoing ranges, etc.).

According to some embodiments, the at least one thermal shunt member isin thermal communication with at least one fluid conduit (e.g., internalpassageway) extending at least partially through an interior of theelongate body, the at least one fluid conduit being configured to placethe electrode in fluid communication with a fluid source to selectivelyremove heat from the electrode assembly and/or tissue of a subjectlocated adjacent the electrode assembly.

According to some embodiments, the at least one thermal shunt membercomprises a thermal diffusivity greater than 1.5 cm²/sec. In someembodiments, the at least one thermal shunt member comprises diamond(e.g., industrial-grade diamond).

According to some embodiments, the second plurality oftemperature-measurement devices is positioned along a plane that issubstantially perpendicular to a longitudinal axis of the distal end ofthe elongate body and spaced proximal to the first plurality oftemperature-measurement devices. In some embodiments, each of thetemperature-measurement devices comprises a thermocouple, a thermistorand/or any other type of temperature sensor or temperature measuringdevice or component. In some embodiments, the first plurality oftemperature-measurement devices comprises at least three (e.g., 3, 4, 5,6, more than 6, etc.) temperature sensors, and wherein the secondplurality of temperature-measurement devices comprises at least three(e.g., 3, 4, 5, 6, more than 6, etc.) temperature sensors.

According to some embodiments, the device further comprises a means forfacilitating high-resolution mapping. In some embodiments, electricallyseparating the first and second electrode portions facilitateshigh-resolution mapping along a targeted anatomical area. In someembodiments, the device further comprises at least one separatorpositioned within the at least one electrically insulating gap. In oneembodiment, the at least one separator contacts a proximal end of thefirst electrode and the distal end of the second electrode portion.

According to some embodiments, the device further comprises at least oneconductor configured to electrically couple an energy delivery module toat least one of the first and second electrodes. In some embodiments,the at least one conductor is electrically coupled to an energy deliverymodule.

According to some embodiments, a frequency of energy provided to thefirst and second electrodes is in the radiofrequency range. In someembodiments, a series impedance introduced across the first and secondelectrodes is lower than: (i) an impedance of a conductor thatelectrically couples the electrodes to an energy delivery module, and(ii) an impedance of a tissue being treated. In some embodiments, thegap width is approximately 0.2 to 1.0 mm (e.g., 0.5 mm, 0.2-0.3,0.3-0.4, 0.4-0.5, 0.5-0.6, 0.6-0.7, 0.7-0.8, 0.8-0.9, 0.9-1.0 mm, valuesbetween the foregoing ranges, less than 0.2 mm, greater than 1 mm,etc.). In some embodiments, the elongate body (e.g., catheter) comprisesat least one irrigation passage, said at least one irrigation passageextending to the first electrode.

According to some embodiments, the at least a second electrode comprisesa second electrode and a third electrode portion, the second electrodeportion positioned axially between the first and third electrodeportions, wherein an electrically insulating gap separates the secondand third electrode portions. In some embodiments, gaps are includedbetween the first and second electrode portions and between the secondand third electrode portions to increase a ratio of mapped tissuesurface to ablated tissue surface. In some embodiments, the ratio isbetween 0.2 and 0.8 (e.g., 0.2-0.3, 0.3-0.4, 0.4-0.5, 0.5-0.6, 0.6-0.7,0.7-0.8, ratios between the foregoing, etc.). In some embodiments, thedevice further comprises a separator positioned within the gap betweenthe second and third electrode portions.

According to some embodiments, a device for mapping and ablating tissuecomprises an elongate body (e.g., a catheter, other medical instrument,etc.) including a proximal end and a distal end, a first electrode (orelectrode portion or section) positioned on the elongate body, at leasta second electrode (or electrode portion or section) positioned adjacentthe first electrode, the first electrode (or electrode portion orsection) and the second electrode (or electrode portion or section)being configured to contact tissue of a subject and deliverradiofrequency energy sufficient to at least partially ablate thetissue, at least one electrically insulating gap positioned between thefirst electrode (or electrode portion or section) and the secondelectrode (or electrode portion or section), the at least oneelectrically insulating gap comprising a gap width separating the firstand second electrodes (or electrode portions or sections), and afiltering element electrically coupling the first electrode (orelectrode portion or section) to the second electrode (or electrodeportion or section) and configured to present a low impedance at afrequency used for delivering ablative energy via the first and secondelectrodes (or electrode portions or sections).

According to some embodiments, the device further comprises a means forfacilitating high-resolution mapping. In some embodiments, electricallyseparating the first and second electrodes (or electrode portions orsections) facilitates high-resolution mapping along a targetedanatomical area (e.g., cardiac tissue). In some embodiments, the devicefurther comprises at least one separator positioned within the at leastone electrically insulating gap. In one embodiment, the at least oneseparator contacts a proximal end of the first electrode (or electrodeportion or section) and the distal end of the second electrode (orelectrode portion or section). In some embodiments, the device furthercomprises at least one conductor configured to electrically couple anenergy delivery module to at least one of the first and secondelectrodes (or electrode portions or sections). In some embodiments, theat least one conductor is electrically coupled to an energy deliverymodule.

According to some embodiments, a frequency of energy provided to thefirst and second electrodes is in the radiofrequency range. In someembodiments, the filtering element comprises a capacitor. In someembodiments, the capacitor comprises a capacitance of 50 to 300 nF(e.g., 100 nF, 50-100, 100-150, 150-200, 200-250, 250-300 nF, valuesbetween the foregoing ranges, etc.). In some embodiments, the capacitorcomprises a capacitance of 100 nF. In some embodiments, a seriesimpedance of lower than about 3 ohms (Ω) (e.g., e.g., 0-1, 1-2, 2-3ohms, values between the foregoing ranges, etc.) is introduced acrossthe first and second electrodes in the operating RF frequency range. Insome embodiments, the operating RF frequency range is 200 kHz to 10 MHz(e.g., 200-300, 300-400, 400-500, 500-600, 600-700, 700-800, 800-900,900-1000 kHz, up to 10 MHz or higher frequencies between the foregoingranges, etc.).

According to some embodiments, a series impedance introduced across thefirst and second electrodes is lower than: (i) an impedance of aconductor that electrically couples the electrodes to an energy deliverymodule, and (ii) an impedance of a tissue being treated. In someembodiments, the gap width is approximately 0.2 to 1.0 mm (e.g., 0.2,0.2-0.3, 0.3-0.4, 0.4-0.5, 0.5-0.6, 0.6-0.7, 0.7-0.8, 0.8-0.9, 0.9-1.0mm, values between the foregoing ranges, less than 0.2 mm, greater than1 mm, etc.). In some embodiments, the gap width is 0.5 mm.

According to some embodiments, the elongate body comprises at least oneirrigation passage, the at least one irrigation passage extending to thefirst electrode. In some embodiments, the first electrode (or electrodeportion or section) comprises at least one outlet port in fluidcommunication with the at least one irrigation passage.

According to some embodiments, the at least a second electrode (orelectrode portion or section) comprises a second electrode (or electrodeportion or section) and a third electrode (or electrode portion orsection), the second electrode (or electrode portion or section) beingpositioned axially between the first and third electrodes (or electrodeportions or sections), wherein an electrically insulating gap separatesthe second and third electrodes (or electrode portions or sections). Insome embodiments, gaps are included between the first and secondelectrodes (or electrode portions or sections) and between the secondand third electrodes (or electrode portions or sections) to increase aratio of mapped tissue surface to ablated tissue surface. In someembodiments, the ratio is between 0.2 and 0.8 (e.g., 0.2-0.3, 0.3-0.4,0.4-0.5, 0.5-0.6, 0.6-0.7, 0.7-0.8, ratios between the foregoing, etc.).In some embodiments, the device further comprising a separatorpositioned within the gap between the second and third electrodes (orelectrode portions or sections).

According to some embodiments, an ablation device comprises a firstelectrode (or electrode portion or section) positioned at a distal endof a catheter, at least a second electrode (or electrode portion orsection) positioned at a location proximal to the first electrode (orelectrode portion or section), the first electrode (or electrode portionor section) and the second electrode (or electrode portion or section)being configured to contact tissue (e.g., cardiac tissue, other targetedanatomical tissue, etc.) of a subject and deliver energy sufficient toat least partially ablate the tissue, an electrically insulating gappositioned between the first electrode (or electrode portion or section)and the second electrode (or electrode portion or section), theelectrically insulating gap comprising a gap width separating the firstand second electrodes (or electrode portions or sections), and afiltering element electrically coupling the first electrode (orelectrode portion or section) to the second electrode (or electrodeportion or section).

According to some embodiments, electrically separating the first andsecond electrodes (or electrode portions or sections) facilitateshigh-resolution mapping along a targeted anatomical area. In someembodiments, the device further comprises at least one separatorpositioned within the at least one electrically insulating gap. Inseveral embodiments, the at least one separator contacts a proximal endof the first electrode (or electrode portion or section) and the distalend of the second electrode (or electrode portion or section).

According to some embodiments, the device additionally comprises atleast one conductor configured to energize at least one of the first andsecond electrodes (or electrode portions or sections). In oneembodiment, the at least one conductor is electrically coupled to anenergy delivery module (e.g., a RF generator).

According to some embodiments, the device further comprises means forconnectivity to an electrophysiology recorder. In some embodiments, thedevice is configured to connect to an electrophysiology recorder.

According to some embodiments, a frequency of energy provided to thefirst and second electrodes is in the radiofrequency (RF) range. In someembodiments, the operating RF frequency range is 200 kHz to 10 MHz(e.g., 200-300, 300-400, 400-500, 500-600, 600-700, 700-800, 800-900,900-1000 kHz, up to 10 MHz or higher frequencies between the foregoingranges, etc.). In some embodiments, the filtering element comprises acapacitor. In some embodiments, the capacitor comprises a capacitance of50 to 300 nF (e.g., 100 nF, 50-100, 100-150, 150-200, 200-250, 250-300nF, values between the foregoing ranges, etc.). In some embodiments, aseries impedance of less than 3 ohms (Ω) (e.g., e.g., 0-1, 1-2, 2-3ohms, values between the foregoing ranges, etc.) is introduced acrossthe first and second electrodes (or electrode portions or sections) at500 kHz.

According to some embodiments, a series impedance introduced across thefirst and second electrodes is lower than: (i) an impedance of aconductor that electrically couples the electrodes to an energy deliverymodule, and (ii) an impedance of a tissue being treated. In someembodiments, the gap width is approximately 0.2 to 1.0 mm (e.g., 0.2,0.2-0.3, 0.3-0.4, 0.4-0.5, 0.5-0.6, 0.6-0.7, 0.7-0.8, 0.8-0.9, 0.9-1.0mm, values between the foregoing ranges, less than 0.2 mm, greater than1 mm, etc.). In one embodiment, the gap width is 0.5 mm.

According to some embodiments, the at least a second electrode (orelectrode portion or section) comprises a second electrode (or electrodeportion or section) and a third electrode (or electrode portion orsection), the second electrode (or electrode portion or section) beingpositioned axially between the first and third electrodes (or electrodeportions or sections), wherein an electrically insulating gap separatesthe second and third electrodes (or electrode portions or sections). Insome embodiments, the a separator is positioned within the gap betweenthe second and third electrodes (or electrode portions or sections). Insome embodiments, gaps are included between the first and secondelectrodes (or electrode portions or sections) and between the secondand third electrodes (or electrode portions or sections) to increase aratio of mapped tissue surface to ablated tissue surface. In someembodiments, the ratio is between 0.2 and 0.8 (e.g., 0.2-0.3, 0.3-0.4,0.4-0.5, 0.5-0.6, 0.6-0.7, 0.7-0.8, ratios between the foregoing, etc.).

According to some embodiments, the system further comprises means forconnectivity to an electrophysiology recorder. In some embodiments, thesystem is configured to connect to an electrophysiology recorder. Insome embodiments, the system comprises an ablation device, and at leastone of (i) a generator for selectively energizing the device, and (ii)an electrophysiology recorder.

According to some embodiments, a method of delivering energy to anablation device comprises energizing a split tip or split sectionelectrode positioned on a catheter (or other medical instrument), thesplit tip or split section electrode comprising a first electrode and asecond electrode (or electrode portions or sections), the firstelectrode and the second electrode being configured to contact tissue ofa subject and deliver energy sufficient to at least partially ablate thetissue, wherein an electrically insulating gap is positioned between thefirst electrode and the second electrode, the electrically insulatinggap comprising a gap width separating the first and second electrodes,wherein a filtering element electrically couples the first electrode tothe second electrode, and wherein electrically separating the first andsecond electrodes facilitates high-resolution mapping along a targetedanatomical area.

According to some embodiments, the method additionally includesreceiving high-resolution mapping data from the first and secondelectrodes (or electrode portions or sections), the high-resolutionmapping data relating to tissue of a subject adjacent the first andsecond electrodes (or electrode portions or sections). In someembodiments, receiving high-resolution mapping data occurs prior to,during or after energizing a split tip electrode positioned on acatheter.

According to some embodiments, a method of mapping tissue of a subjectincludes receiving high-resolution mapping data using a split-tip orsplit-section electrode, said split-tip or split-section electrodecomprising first and second electrodes positioning a split-sectionelectrode located on a catheter, the split-tip or split-sectionelectrode comprising a first electrode and a second electrode separatedby an electrically insulating gap, wherein a filtering elementelectrically couples the first electrode to the second electrode in theoperating RF range, and wherein electrically insulating the first andsecond electrodes facilitates high-resolution mapping along a targetedanatomical area.

According to some embodiments, the method additionally includesenergizing at least one of the first and second electrodes to deliverenergy sufficient to at least partially ablate the tissue of thesubject. In some embodiments, the high-resolution mapping data relatesto tissue of a subject adjacent the first and second electrodes. In someembodiments, receiving high-resolution mapping data occurs prior to,during or after energizing a split tip or a split section electrodepositioned on a catheter.

According to some embodiments, a separator is positioned within the atleast one electrically insulating gap. In some embodiments, the at leastone separator contacts a proximal end of the first electrode and thedistal end of the second electrode. In some embodiments, the first andsecond electrodes are selectively energized using at least one conductorelectrically coupled to an energy delivery module. In some embodiments,the mapping data is provided to an electrophysiology recorder.

According to some embodiments, a frequency of energy provided to thefirst and second electrodes is in the radiofrequency (RF) range. In someembodiments, the filtering element comprises a capacitor.

According to some embodiments, a frequency of energy provided to thefirst and second electrodes is in the radiofrequency (RF) range. In someembodiments, the operating RF frequency range is 200 kHz to 10 MHz(e.g., 200-300, 300-400, 400-500, 500-600, 600-700, 700-800, 800-900,900-1000 kHz, up to 10 MHz or higher frequencies between the foregoingranges, etc.). In some embodiments, the filtering element comprises acapacitor. In some embodiments, the capacitor comprises a capacitance of50 to 300 nF (e.g., 100 nF, 50-100, 100-150, 150-200, 200-250, 250-300nF, values between the foregoing ranges, etc.). In some embodiments, aseries impedance of less than 3 ohms (Ω) (e.g., e.g., 0-1, 1-2, 2-3ohms, values between the foregoing ranges, etc.) is introduced acrossthe first and second electrodes (or electrode portions or sections) at500 kHz.

According to some embodiments, a series impedance introduced across thefirst and second electrodes is lower than: (i) an impedance of aconductor that electrically couples the electrodes to an energy deliverymodule, and (ii) an impedance of a tissue being treated. In someembodiments, the gap width is approximately 0.2 to 1.0 mm (e.g., 0.2,0.2-0.3, 0.3-0.4, 0.4-0.5, 0.5-0.6, 0.6-0.7, 0.7-0.8, 0.8-0.9, 0.9-1.0mm, values between the foregoing ranges, less than 0.2 mm, greater than1 mm, etc.). In one embodiment, the gap width is 0.5 mm.

According to some embodiments, a kit for ablation and high-resolutionmapping of cardiac tissue, comprising a device for high-resolutionmapping, the device further being configured to provide ablative energyto targeted tissue, the device comprising an elongate body (e.g.,catheter, other medical instrument, etc.) comprising a proximal end anda distal end, the elongate body comprising an electrode assembly, theelectrode assembly comprising a first and second high-resolutionportions, the first high-resolution electrode portion positioned on theelongate body, the second electrode portion being positioned adjacentthe first electrode portion, the first and second electrode portionsbeing configured to contact tissue of a subject, and at least oneelectrically insulating gap positioned between the first electrodeportion and the second electrode portion, the at least one electricallyinsulating gap comprising a gap width separating the first and secondelectrode portions, wherein the first electrode portion is configured toelectrically couple to the second electrode portion using a filteringelement, wherein the filtering element is configured to present a lowimpedance at a frequency used for delivering ablative energy via thefirst and second electrode portions, and wherein the device isconfigured to be positioned within targeted tissue of the subject toobtain high-resolution mapping data related to said tissue when ablativeenergy is not delivered to the first and second electrode portions. Thekit further comprises an energy delivery module configured to generateenergy for delivery to the electrode assembly, and a processorconfigured to regulate the delivery of energy from the energy deliverymodule to the electrode assembly.

According to some embodiments, a kit for ablation and high-resolutionmapping of cardiac tissue comprises an ablation device, an energydelivery module (e.g., a generator) configured to generate energy fordelivery to the electrode assembly, and a processor configured toregulate the delivery of energy from the energy delivery module to theelectrode assembly. In some embodiments, the energy delivery modulecomprises a RF generator. In some embodiments, the energy deliverymodule is configured to couple to the device.

According to some embodiments, a generator for selectively deliveringenergy to an ablation device comprises an energy delivery moduleconfigured to generate ablative energy for delivery to an ablationdevice, and a processor configured to regulate the delivery of energyfrom the energy delivery module to the ablation device.

According to some embodiments, an ablation device comprises an elongatebody (e.g., catheter, other medical instrument, etc.) comprising adistal end, an electrode positioned at the distal end of the elongatebody, and at least one thermal shunt member placing a heat absorptionelement in thermal communication with the electrode to selectivelyremove heat from at least one of the electrode and tissue being treatedby the electrode when the electrode is activated, wherein the at leastone thermal shunt member extends at least partially through an interiorof the electrode to dissipate and remove heat from the electrode duringuse.

According to some embodiments, the at least one thermal shunt member isin thermal communication with at least one fluid conduit extending atleast partially through an interior of the elongate body, the at leastone fluid conduit being configured to place the electrode in fluidcommunication with a fluid source to selectively remove heat from theelectrode and/or tissue of a subject located adjacent the electrode. Insome embodiments, a fluid conduit or passage extends at least partiallythrough an interior of the elongate body. In some embodiments, the fluidconduit or passage extends at least partially through the at least onethermal shunt member. In several configurations, the at least onethermal shunt member is at least partially in thermal communication witha thermally convective fluid. In some embodiments,

a flow rate of the thermally convective fluid is less than 15 ml/min inorder to maintain a desired temperature along the electrode during anablation procedure. In some embodiments, a flow rate of the thermallyconvective fluid is approximately less than 10 ml/min in order tomaintain a desired temperature along the electrode during an ablationprocedure. In some embodiments, a flow rate of the thermally convectivefluid is approximately less than 5 ml/min in order to maintain a desiredtemperature along the electrode during an ablation procedure. In someembodiments, the desired temperature along the electrode during anablation procedure is 60 degrees C. In some embodiments, the thermallyconvective fluid comprises blood and/or another bodily fluid.

According to some embodiments, the at least one fluid conduit is indirect thermal communication with the at least one thermal shunt member.In some embodiments, the at least one fluid conduit is not in directthermal communication with the at least one thermal shunt member. Insome embodiments, the at least one fluid conduit comprises at least oneopening, wherein the at least one opening places irrigation fluidpassing through the at least one fluid conduit in direct physicalcontact with at least a portion of the at least one thermal shuntmember. In some embodiments, the at least one opening is located along aperforated portion of the at least one conduit, wherein the perforatedportion of the at least one conduit is located distally to theelectrode. In some embodiments, the at least one fluid conduit is influid communication only with exit ports located along the distal end ofthe elongate body. In several configurations, the at least one fluidconduit directly contacts the at least one thermal shunt member. In someembodiments, the at least one fluid conduit does not contact the atleast one thermal shunt member.

According to some embodiments, the at least one thermal shunt membercomprises a thermal diffusivity greater than 1.5 cm²/sec. In someembodiments, the at least one thermal shunt member comprises diamond(e.g., an industrial-grade diamond). In other embodiments, the at leastone thermal shunt member comprises a carbon-based material (e.g.,Graphene, silica, etc.). In some embodiments, a temperature of the atleast one thermal shunt member does not exceed 60 to 62 degrees Celsiuswhile maintaining a desired temperature along the electrode during anablation procedure. In some embodiments, the desired temperature alongthe electrode during an ablation procedure is 60 degrees C.

According to some embodiments, the electrode comprises a radiofrequency(RF) electrode. In some embodiments, the electrode comprises a split-tipelectrode. In several configurations, the split-tip electrode comprisesa first electrode portion and at least a second electrode portion,wherein an electrically insulating gap is located between the firstelectrode portion and the at least a second electrode portion tofacilitate high-resolution mapping along a targeted anatomical area.

According to some embodiments, at least a portion of the at least onethermal shunt member extends to an exterior of the catheter adjacent theproximal end of the electrode. In some embodiments, at least a portionof the at least one thermal shunt member extends to an exterior of thecatheter adjacent the distal end of the electrode. In some embodiments,at least a portion of the at least one thermal shunt member extendsproximally relative to the proximal end of the electrode. In someembodiments, the at least one thermal shunt member comprises a disk orother cylindrically-shaped member. In some embodiments, the at least onethermal shunt member comprises at least one extension member extendingoutwardly from a base member.

According to some embodiments, the at least one fluid conduit comprisesat least one fluid delivery conduit and at least one fluid returnconduit, wherein the fluid is at least partially circulated through aninterior of the elongate body via the at least one fluid deliveryconduit and the at least one fluid return conduit, wherein the at leastone fluid conduit is part of a closed-loop or non-open cooling system.In some embodiments, the elongate body comprises a cooling chamber alonga distal end of the elongate body, wherein the cooling chamber isconfigured to be in fluid communication with the at least one fluidconduit. In some embodiments, the at least one fluid conduit comprises ametallic material, an alloy and/or the like. In some embodiments, theelongate body does not comprise a fluid conduit. In some embodiments, aninterior of a distal end of the elongate body comprises an interiormember generally along a location of the electrode. In some embodiments,the interior member comprises at least one thermally conductive materialconfigured to dissipate and/or transfer heat generated by the electrode.

According to some embodiments, an ablation device comprises an elongatebody (e.g., catheter, other medical instrument, etc.) including a distalend, an ablation member positioned at the distal end of the elongatebody, and at least one thermal shunt member placing a heat shuntingelement in thermal communication with the electrode to selectivelyremove heat from at least a portion of the electrode and/or tissue beingtreated by the electrode when the electrode is activated, wherein theheat shunting element of the at least one thermal shunt extends at leastpartially through an interior of the ablation member to help remove anddissipate heat generated by the ablation member during use.

According to several embodiments, the at least one thermal shunt memberis in thermal communication with at least one fluid conduit or passageextending at least partially through an interior of the elongate body,the at least one fluid conduit or passage being configured to place theablation member in fluid communication with a fluid source toselectively remove heat from the ablation member and/or tissue of asubject located adjacent the ablation member. In some embodiments, theat least one thermal shunt member comprises at least one fluid conduitor passage extending at least partially through an interior of theelongate body. In some embodiments, the at least one thermal shuntmember does not comprise a fluid conduit or passage extending at leastpartially through an interior of the elongate body. In some embodiments,an interior of the distal end of the elongate body comprises an interiormember generally along a location of the ablation member. In severalconfigurations, the interior member comprises at least one thermallyconductive material configured to dissipate and/or transfer heatgenerated by the ablation member.

According to some embodiments, the ablation member comprises aradiofrequency (RF) electrode. In some embodiments, the ablation membercomprises one of a microwave emitter, an ultrasound transducer and acryoablation member.

According to some embodiments, the at least one thermal shunt membercomprises a thermal diffusivity greater than 1.5 cm²/sec (e.g., greaterthan 1.5 cm²/sec or 5 cm²/sec (e.g., 1.5-2, 2-2.5, 2.5-3, 3-4, 4-5, 5-6,6-7, 7-8, 8-9, 9-10, 10-11, 11-12, 12-13, 13-14, 14-15, 15-20 cm²/sec,values between the foregoing ranges, greater than 20 cm²/sec). In somearrangements, the at least one thermal shunt member comprises a thermaldiffusivity greater than 5 cm²/sec. In some embodiments, the at leastone thermal shunt member comprises a diamond (e.g., an industrial-gradediamond). In some embodiments, the at least one thermal shunt membercomprises a carbon-based material (e.g., Graphene, silica, etc.). Insome embodiments, the radiofrequency (RF) electrode comprises asplit-tip RF electrode or other high-resolution electrode.

According to some embodiments, the at least one fluid conduit or passageis in direct thermal communication with the at least one thermal shuntmember. In some embodiments, the at least one irrigation conduit is notin direct thermal communication with the at least one thermal shuntmember. In some arrangements, the at least one fluid conduit or passagedirectly contacts the at least one thermal shunt member. In someembodiments, the at least one fluid conduit or passage does not contactthe at least one thermal shunt member. In some embodiments, the at leastone fluid conduit or passage comprises at least one opening, wherein theat least one opening places irrigation fluid passing through the atleast one fluid conduit or passage in direct physical contact with atleast a portion of the at least one thermal shunt member. In someembodiments, the at least one opening is located along a perforatedportion of the at least one conduit or passage, wherein the perforatedportion of the at least one conduit or passage is located distally tothe electrode.

According to some embodiments, at least a portion of the at least onethermal shunt member extends to an exterior of the catheter adjacent theproximal end of the ablation member. In some embodiments, at least aportion of the at least one thermal shunt member extends to an exteriorof the catheter adjacent the distal end of the ablation member. In someembodiments, at least a portion of the at least one thermal shunt memberextends proximally relative to the proximal end of the ablation member.In some embodiments, the at least one thermal shunt member comprises adisk or other cylindrically-shaped member. In several configurations,the at least one thermal shunt member comprises at least one extensionmember extending outwardly from a base member. In some embodiments, theat least one extension member comprises at least one of a fin, a pin ora wing. In some embodiments, the at least one fluid conduit or passagecomprises a metallic material.

According to some embodiments, a method of heat removal from an ablationmember during a tissue treatment procedure includes activating anablation system, the system comprising an elongate body (e.g., catheter,other medical instrument, etc.) comprising a distal end, an ablationmember positioned at the distal end of the elongate body, wherein theelongate body of the ablation system comprises at least one thermalshunt member along its distal end, wherein the at least one thermalshunt member extends at least partially through an interior of theablation member, and at least partially removing heat generated by theablation member along the distal end of the elongate body via the atleast one thermal shunt member so as to reduce the likelihood oflocalized hot spots along the distal end of the elongate body.

According to some embodiments, the elongate body further comprises atleast one fluid conduit or passage extending at least partially throughan interior of the elongate body, wherein the method further comprisesdelivering fluid through the at least one fluid conduit or passage,wherein the at least one thermal shunt member places the at least onefluid conduit or passage in thermal communication with a proximalportion of the ablation member to selectively remove heat from theproximal portion of the ablation member when the electrode is activated,wherein the at least one fluid conduit or passage is configured to placethe ablation member in fluid communication with a fluid source toselectively remove heat from the ablation member and/or tissue of asubject located adjacent the ablation member.

According to some embodiments, the elongate body is advanced to a targetanatomical location of the subject through a bodily lumen of thesubject. In some embodiments, the bodily lumen of the subject comprisesa blood vessel, an airway or another lumen of the respiratory tract, alumen of the digestive tract, a urinary lumen or another bodily lumen.In some embodiments, the ablation member comprises a radiofrequency (RF)electrode. In other arrangements, the ablation member comprises one of amicrowave emitter, an ultrasound transducer and a cryoablation member.

According to some embodiments, the at least one thermal shunt membercomprises a thermal diffusivity greater than 1.5 cm²/sec (e.g., greaterthan 1.5 cm²/sec or 5 cm²/sec (e.g., 1.5-2, 2-2.5, 2.5-3, 3-4, 4-5, 5-6,6-7, 7-8, 8-9, 9-10, 10-11, 11-12, 12-13, 13-14, 14-15, 15-20 cm²/sec,values between the foregoing ranges, greater than 20 cm²/sec). In somearrangements, the at least one thermal shunt member comprises a thermaldiffusivity greater than 5 cm²/sec. In some embodiments, the at leastone thermal shunt member comprises a diamond (e.g., an industrial-gradediamond). In some embodiments, the at least one thermal shunt membercomprises a carbon-based material (e.g., Graphene, silica, etc.). Insome embodiments, the radiofrequency (RF) electrode comprises asplit-tip RF electrode or other high-resolution electrode. In someembodiments, the method additionally includes obtaining at least onehigh-resolution image of the target anatomical locations of the subjectadjacent the ablation member.

According to some embodiments, the at least one fluid conduit or passageis in direct thermal communication with the at least one thermal shuntmember. In some embodiments, the at least one irrigation conduit is notin direct thermal communication with the at least one thermal shuntmember. According to some embodiments, the at least one fluid conduit orpassage directly contacts the at least one thermal shunt member. In someembodiments, the at least one fluid conduit or passage does not contactthe at least one thermal shunt member. In some embodiments, deliveringfluid through the at least one fluid conduit or passage comprisesdelivering fluid to and through the distal end of the catheter in anopen irrigation system. In several configurations, delivering fluidthrough the at least one fluid conduit or passage includes circulatingfluid through the distal end of the catheter adjacent the ablationmember in a closed fluid cooling system.

According to some embodiments, the elongate body of the ablation systemdoes not comprise any fluid conduits or passages. In one embodiment, theelongate body comprises an interior member. In some embodiments, theinterior member comprises a thermally conductive material that is inthermal communication with the at least one thermal shunt member to helpdissipate and distribute heat generated by the ablation member duringuse. In some embodiments, at least a portion of the at least one thermalshunt member extends to an exterior of the catheter adjacent theproximal end of the ablation member. In some embodiments, at least aportion of the at least one thermal shunt member extends proximally tothe proximal end of the ablation member. In some embodiments, at least aportion of the at least one thermal shunt member extends distally to theproximal end of the ablation member such that at least a portion of theat least one thermal shunt member is located along a length of theablation member. In several configurations, the at least one thermalshunt member comprises a disk or other cylindrically-shaped member. Insome arrangements, the at least one thermal shunt member comprises atleast one extension member extending outwardly from a base member. Insome embodiments, the at least one extension member comprises at leastone of a fin, a pin, a wing and/or the like.

According to some embodiments, a system comprises means for connectivityto an electrophysiology recorder. In some embodiments, the system isconfigured to connect to an electrophysiology recorder. In someembodiments, the system further comprises at least one of (i) agenerator for selectively energizing the device, and (ii) anelectrophysiology recorder. In some embodiments, the system furthercomprises both (i) a generator for selectively energizing the device,and (ii) an electrophysiology recorder.

According to some embodiments, a system for delivering energy totargeted tissue of a subject includes a catheter having ahigh-resolution electrode (e.g., a split-tip electrode). The split-tipelectrode can include two or more electrodes or electrode portions thatare separated by an electrically-insulating gap. A filtering element canelectrically couple the first and second electrodes or electrodeportions, or any adjacent electrode sections (e.g., in a circumferentialor radial arrangement) and can be configured to present a low impedanceat a frequency used for delivering ablative energy via the first andsecond electrodes or electrode portions. In some embodiments,electrically separating the first and second electrodes, or electrodeportions (e.g., in a circumferential or radial arrangement), facilitateshigh-resolution mapping along a targeted anatomical area. The cathetercan further include a plurality of temperatures sensors (e.g.,thermocouples) that are thermally insulated from the electrode and areconfigured to detect tissue temperature at a depth. The catheter canalso include one or more thermal shunt members and/or components fortransferring heat away from the electrode and/or the tissue beingtreated. In some embodiments, such thermal shunt members and/orcomponents include diamond (e.g., industrial diamond) and/or othermaterials with favorable thermal diffusivity characteristics. Further,the system can be configured to detect whether and to what extentcontact has been achieved between the electrode and targeted tissue.

According to some embodiments, an energy delivery device (e.g., ablationdevice) comprises an elongate body (e.g., a catheter) comprising aproximal end and a distal end, a first electrode (e.g., radiofrequencyelectrode) positioned at the distal end of the elongate body, and one ormore second electrodes (e.g., radiofrequency electrodes) positioned at alocation proximal to the first electrode, the first electrode and thesecond electrode being configured to contact tissue of a subject anddeliver radiofrequency energy sufficient to at least partially ablatethe tissue. In alternative embodiments, the electrodes are distributedor otherwise located circumferentially around the catheter (e.g., alongfour quadrant sections distributed around the catheter shaftcircumference separated by gaps). In other embodiments, the catheter mayhave additional support structures and may employ multiple electrodesdistributed on the support structures. The device further comprises atleast one electrically insulating gap positioned between the firstelectrode and the second electrode or the sections of circumferentialelectrodes, the at least one electrically insulating gap comprising agap width separating the first and second electrodes, and a band-passfiltering element electrically coupling the first electrode to thesecond electrode, or any adjacent electrode sections (e.g., in acircumferential or radial arrangement), and configured to present a lowimpedance at a frequency used for delivering ablative energy via thefirst and second electrodes. In some embodiments, electricallyseparating the first and second electrodes, or electrode sections (e.g.,in a circumferential or radial arrangement), facilitates high-resolutionmapping along a targeted anatomical area. In some embodiments, the ratioof ablated tissue surface to that of mapped tissue is enhanced (e.g.,optimized).

Several embodiments disclosed in the present application areparticularly advantageous because they include one, more or all of thefollowing benefits: a system configured to deliver energy (e.g.,ablative or other type of energy) to anatomical tissue of a subject andconfigured for high-resolution mapping; a system configured to deliverenergy to anatomical tissue of a subject and configured to detect theeffectiveness of the resulting treatment procedure using itshigh-resolution mapping capabilities and functions; a split-tip orsplit-section design configured to be energized as a unitary tip orsection to more uniformly provide energy to targeted anatomical tissueof a subject and/or the like.

According to some embodiments, the device further comprises a separatorpositioned within the at least one electrically insulating gap. In someembodiments, the at least one separator contacts a proximal end of thefirst electrode and the distal end of the second electrode. In someembodiments, the separator contacts, at least partially, a side of oneelectrode section and an opposing side of the adjacent electrodesection. In one embodiment, the first and second electrodes and theseparator are cylindrical. In one embodiment, the outer diameter of theelectrodes and the separator are equal. In some embodiments, the firstand second electrodes include quadrants or other sections that arecircumferentially distributed on the catheter shaft. In someembodiments, the first and second electrodes comprise other geometriesthat make suitable for distribution on a catheter shaft and also beseparated by a narrow non-conductive gap. In some embodiments, thedevice further comprises at least one conductor (e.g., wire, cable,etc.) configured to electrically couple an energy delivery module (e.g.,a RF or other generator) to at least one of the first and secondelectrodes. In some embodiments, the device further comprises one ormore additional conductors connected to each of the first and secondelectrodes for distributing signals (e.g., cardiac signals) picked up bysaid electrodes to an electrophysiology (EP) recorder.

According to some embodiments, a device additionally includes anelectrophysiology recorder. In some embodiments, a frequency of energyprovided to the first and second electrodes is in an operatingradiofrequency (RF) range (e.g., approximately 300 kHz to 10 MHz).

According to some embodiments, the band-pass filtering element comprisesa capacitor. In some embodiments, the capacitor comprises a capacitanceof 50 to 300 nF (e.g., 100 nF, 50-100, 100-150, 150-200, 200-250,250-300 nF, values between the foregoing ranges, etc.), depending, e.g.,on the operating frequency used to deliver ablative energy. In someembodiments, a series impedance of about 3 ohms (Ω) or less than about 3ohms (e.g., 0-1, 1-2, 2-3 ohms, values between the foregoing ranges,etc.) is introduced between the first and second electrodes in theoperating RF frequency range (e.g., 300 kHz to 10 MHz). For example, alower capacitance value (e.g. 5-10 nF) may be used at a higher frequencyrange (e.g. 10 MHz). In some embodiments, a 100 nF capacitance value maybe well-suited for applications in the 500 kHz frequency range. In someembodiments, a series impedance introduced across the first and secondelectrodes is lower than: (i) an impedance of a conductor thatelectrically couples the electrodes to an energy delivery module, and(ii) an impedance of a tissue being treated. In some embodiments, thedevice further comprises a band-pass filtering element electricallycoupling the second electrode to the third electrode, or any adjacentelectrode sections (e.g., in a circumferential or radial arrangement),and configured to present a low impedance at a frequency used fordelivering ablative energy via the second and third electrodes.

According to some embodiments, the gap width between the first andsecond electrodes is approximately 0.2 to 1.0 mm (e.g., 0.5 mm). In someembodiments, the elongate body comprises at least one irrigationpassage, said at least one irrigation passage extending to the firstelectrode. In one embodiment, the first electrode comprises at least oneoutlet port in fluid communication with the at least one irrigationpassage.

According to some embodiments, the device further comprises a thirdelectrode, wherein the second electrode is positioned axially betweenthe first and third electrodes, wherein an electrically insulating gapseparates the second and third electrodes. In some embodiments, thedevice further comprises a separator positioned within the gap betweenthe second and third electrodes.

According to some embodiments, a system comprises an ablation deviceaccording to any of the embodiments disclosed herein. In someembodiments, the system additionally comprises means for connectivity toan electrophysiology recorder. In some embodiments, the system isconfigured to connect to an electrophysiology recorder. In someembodiments, the system further comprises at least one of (i) agenerator for selectively energizing the device, and (ii) anelectrophysiology recorder.

According to some embodiments, a method of simultaneously deliveringenergy to an ablation device and mapping tissue of a subject comprisesenergizing a split-tip or split-section electrode being separated by anon-conductive gap from the first electrode and a second electrode, thesecond electrode positioned at a location proximal to the firstelectrode, the first electrode and the second electrode being configuredto contact tissue of a subject to deliver energy sufficient to at leastpartially ablate the tissue and to receive high-resolution mapping data,the high-resolution mapping data relating to tissue of a subjectadjacent the first and second electrodes. In some embodiments, anelectrically insulating gap is positioned between the first electrodeand the second electrode, the electrically insulating gap comprising agap width separating the first and second electrodes. In someembodiments, a filtering element electrically couples the firstelectrode to the second electrode only in the operating RF frequencyrange. In one embodiment, electrically separating the first and secondelectrodes facilitates high-resolution mapping along a targetedanatomical area.

According to some embodiments, a separator is positioned within the atleast one electrically insulating gap. In one embodiment, the at leastone separator contacts a proximal end of the first electrode and thedistal end of the second electrode.

According to some embodiments, the mapping data is provided to anelectrophysiology recorder. In some embodiments, a frequency of energyprovided to the first and second electrodes is in the radiofrequencyrange.

According to some embodiments, the filtering element comprises acapacitor. In one embodiment, the capacitor comprises a capacitance of50 to 300 nF (e.g., 100 nF), depending on, e.g., the operating frequencyused for ablative energy. In some embodiments, a series impedance ofabout 3 ohms (Ω) is introduced across the first and second electrodes at500 kHz. In some embodiments, a series impedance introduced across thefirst and second electrodes is lower than: (i) an impedance of aconductor that electrically couples the electrodes to an energy deliverymodule, and (ii) an impedance of a tissue being treated.

According to some embodiments, the gap width is approximately 0.2 to 1.0mm. In one embodiment, the gap width is 0.5 mm.

According to some embodiments, an ablation device comprises an elongatebody (e.g., catheter, other medical instrument, etc.) comprising adistal end, an electrode positioned at the distal end of the elongatebody and at least one thermal shunt member placing a heat absorptionelement in thermal communication with the electrode to selectivelyremove heat from at least one of the electrode and tissue being treatedby the electrode when the electrode is activated, wherein the at leastone thermal shunt member extends at least partially through an interiorof the electrode to dissipate and remove heat from the electrode duringuse. In some embodiments, the at least one thermal shunt member is inthermal communication with at least one fluid conduit extending at leastpartially through an interior of the elongate body, the at least onefluid conduit being configured to place the electrode in fluidcommunication with a fluid source to selectively remove heat from theelectrode and/or tissue of a subject located adjacent the electrode. Insome embodiments, a fluid conduit or passage extends at least partiallythrough an interior of the elongate body. In one embodiment, the fluidconduit or passage extends at least partially through the at least onethermal shunt member. In some embodiments, the at least one thermalshunt member is at least partially in thermal communication with athermally convective fluid. In some embodiments, the thermallyconvective fluid comprises blood and/or another bodily fluid.

According to some embodiments, a flow rate of the thermally convectivefluid is less than 15 ml/min in order to maintain a desired temperaturealong the electrode during an ablation procedure. In some embodiments, aflow rate of the thermally convective fluid is approximately less than10 ml/min in order to maintain a desired temperature along the electrodeduring an ablation procedure. In some embodiments, a flow rate of thethermally convective fluid is approximately less than 5 ml/min in orderto maintain a desired temperature along the electrode during an ablationprocedure. According to some embodiments, the desired temperature alongthe electrode during an ablation procedure is 60 degrees C.

According to some embodiments, the at least one thermal shunt membercomprises a thermal diffusivity greater than 1.5 cm²/sec or 5 cm²/sec(e.g., 1.5-2, 2-2.5, 2.5-3, 3-4, 4-5, 5-6, 6-7, 7-8, 8-9, 9-10, 10-11,11-12, 12-13, 13-14, 14-15, 15-20 cm²/sec, values between the foregoingranges, greater than 20 cm²/sec). In some embodiments, the at least onethermal shunt member comprises diamond (e.g., an industrial-gradediamond). In some embodiments, the at least one thermal shunt membercomprises a carbon-based material. In some embodiments, the at least onethermal shunt member comprises at least one of Graphene and silica.

According to some embodiments, a temperature of the at least one thermalshunt member does not exceed 60 to 62 degrees Celsius while maintaininga desired temperature along the electrode during an ablation procedure.In some embodiments, the desired temperature along the electrode duringan ablation procedure is 60 degrees C.

According to some embodiments, the electrode comprises a radiofrequency(RF) electrode. In some embodiments, the electrode comprises a split-tipelectrode. In some embodiments, the split-tip electrode comprises afirst electrode portion and at least a second electrode portion, whereinan electrically insulating gap is located between the first electrodeportion and the at least a second electrode portion to facilitatehigh-resolution mapping along a targeted anatomical area.

According to some embodiments, the at least one fluid conduit is indirect thermal communication with the at least one thermal shunt member.In some embodiments, the at least one fluid conduit is not in directthermal communication with the at least one thermal shunt member. Insome embodiments, the at least one fluid conduit comprises at least oneopening, wherein the at least one opening places irrigation fluidpassing through the at least one fluid conduit in direct physicalcontact with at least a portion of the at least one thermal shuntmember. In some embodiments, the at least one opening is located along aperforated portion of the at least one conduit, wherein the perforatedportion of the at least one conduit is located distally to theelectrode. In one embodiment, the at least one fluid conduit is in fluidcommunication only with exit ports located along the distal end of theelongate body. In some embodiments, the at least one fluid conduitdirectly contacts the at least one thermal shunt member. In someembodiments, the at least one fluid conduit does not contact the atleast one thermal shunt member. In some embodiments, at least a portionof the at least one thermal shunt member extends to an exterior of thecatheter adjacent the proximal end of the electrode. In one embodiment,at least a portion of the at least one thermal shunt member extends toan exterior of the catheter adjacent the distal end of the electrode. Incertain embodiments, at least a portion of the at least one thermalshunt member extends proximally relative to the proximal end of theelectrode. In some embodiments, the at least one thermal shunt membercomprises a disk or other cylindrically-shaped member.

According to some embodiments, an ablation device comprises an elongatebody (e.g., catheter, other medical instrument, etc.) comprising adistal end, an ablation member positioned at the distal end of theelongate body and at least one thermal shunt member placing a heatshunting element in thermal communication with the electrode toselectively remove heat from at least a portion of the electrode and/ortissue being treated by the electrode when the electrode is activated,wherein the heat shunting element of the at least one thermal shuntextends at least partially through an interior of the ablation member tohelp remove and dissipate heat generated by the ablation member duringuse. In some embodiments, the at least one thermal shunt member is inthermal communication with at least one fluid conduit or passageextending at least partially through an interior of the elongate body,the at least one fluid conduit or passage being configured to place theablation member in fluid communication with a fluid source toselectively remove heat from the ablation member and/or tissue of asubject located adjacent the ablation member.

According to some embodiments, the at least one thermal shunt membercomprises at least one fluid conduit or passage extending at leastpartially through an interior of the elongate body. In some embodiments,the at least one thermal shunt member does not comprise a fluid conduitor passage extending at least partially through an interior of theelongate body. In some embodiments, an interior of the distal end of theelongate body comprises an interior member generally along a location ofthe ablation member. In one embodiment, the interior member comprises atleast one thermally conductive material configured to dissipate and/ortransfer heat generated by the ablation member.

According to some embodiments, the ablation member comprises aradiofrequency (RF) electrode. In some embodiments, the ablation membercomprises one of a microwave emitter, an ultrasound transducer and acryoablation member.

According to some embodiments, the at least one thermal shunt membercomprises at least one extension member extending outwardly from a basemember. In some embodiments, the at least one fluid conduit comprises atleast one fluid delivery conduit and at least one fluid return conduit,wherein the fluid is at least partially circulated through an interiorof the elongate body via the at least one fluid delivery conduit and theat least one fluid return conduit, wherein the at least one fluidconduit is part of a closed-loop or non-open cooling system. In someembodiments, the elongate body comprises a cooling chamber along adistal end of the elongate body, wherein the cooling chamber isconfigured to be in fluid communication with the at least one fluidconduit. In some embodiments, the at least one fluid conduit comprisesat least one of a metallic material and an alloy. In some embodiments,the elongate body does not comprise a fluid conduit. In one embodiment,an interior of a distal end of the elongate body comprises an interiormember generally along a location of the electrode. In some embodiments,the interior member comprises at least one thermally conductive materialconfigured to dissipate and/or transfer heat generated by the electrode.

According to some embodiments, a method of heat removal from an ablationmember during a tissue treatment procedure comprises activating anablation system, the system comprising an elongate body comprising adistal end, an ablation member positioned at the distal end of theelongate body, wherein the elongate body of the ablation systemcomprises at least one thermal shunt member along its distal end,wherein the at least one thermal shunt member extends at least partiallythrough an interior of the ablation member, and at least partiallyremoving heat generated by the ablation member along the distal end ofthe elongate body via the at least one thermal shunt member so as toreduce the likelihood of localized hot spots along the distal end of theelongate body.

According to some embodiments, the elongate body (e.g., catheter,medical instrument, etc.) further comprises at least one fluid conduitor passage extending at least partially through an interior of theelongate body, the method further comprising delivering fluid throughthe at least one fluid conduit or passage, wherein the at least onethermal shunt member places the at least one fluid conduit or passage inthermal communication with a proximal portion of the ablation member toselectively remove heat from the proximal portion of the ablation memberwhen the electrode is activated, wherein the at least one fluid conduitor passage is configured to place the ablation member in fluidcommunication with a fluid source to selectively remove heat from theablation member and/or tissue of a subject located adjacent the ablationmember.

According to some embodiments, the elongate body is advanced to a targetanatomical location of the subject through a bodily lumen of thesubject. In some embodiments, the bodily lumen of the subject comprisesa blood vessel, an airway or another lumen of the respiratory tract, alumen of the digestive tract, a urinary lumen or another bodily lumen.In some embodiments, the ablation member comprises a radiofrequency (RF)electrode. In some embodiments, the ablation member comprises one of amicrowave emitter, an ultrasound transducer and a cryoablation member.In some embodiments, the at least one thermal shunt member comprises athermal diffusivity greater than 1.5 cm²/sec or 5 cm²/sec (e.g., 1.5-2,2-2.5, 2.5-3, 3-4, 4-5, 5-6, 6-7, 7-8, 8-9, 9-10, 10-11, 11-12, 12-13,13-14, 14-15, 15-20 cm²/sec, values between the foregoing ranges,greater than 20 cm²/sec). In some embodiments, the at least one thermalshunt member comprises diamond (e.g., an industrial-grade diamond). Insome embodiments, the at least one thermal shunt member comprises acarbon-based material. In some embodiments, the at least one thermalshunt member comprises at least one of Graphene and silica.

According to some embodiments, the radiofrequency (RF) electrodecomprises a split-tip RF electrode. In some embodiments, the methodfurther comprises obtaining at least one high-resolution image of thetarget anatomical locations of the subject adjacent the ablation member.In some embodiments, the at least one fluid conduit or passage is indirect thermal communication with the at least one thermal shunt member.In some embodiments, the at least one irrigation conduit is not indirect thermal communication with the at least one thermal shunt member.In some embodiments, the at least one fluid conduit or passage directlycontacts the at least one thermal shunt member. In one embodiment, theat least one fluid conduit or passage does not contact the at least onethermal shunt member. In certain embodiments, delivering fluid throughthe at least one fluid conduit or passage comprises delivering fluid toand through the distal end of the catheter in an open irrigation system.In some embodiments, delivering fluid through the at least one fluidconduit or passage comprises circulating fluid through the distal end ofthe catheter adjacent the ablation member in a closed fluid coolingsystem.

According to some embodiments, the elongate body (e.g., catheter,medical instrument, etc.) of the ablation system does not comprise anyfluid conduits or passages. In some embodiments, the distal end of theelongate body comprises an interior member. In some embodiments, theinterior member comprises a thermally conductive material that is inthermal communication with the at least one thermal shunt member to helpdissipate and distribute heat generated by the ablation member duringuse. In some embodiments, at least a portion of the at least one thermalshunt member extends to an exterior of the catheter adjacent theproximal end of the ablation member. In one embodiment, at least aportion of the at least one thermal shunt member extends proximally tothe proximal end of the ablation member. In some embodiments, at least aportion of the at least one thermal shunt member extends distally to theproximal end of the ablation member such that at least a portion of theat least one thermal shunt member is located along a length of theablation member. In some embodiments, the at least one thermal shuntmember comprises a disk or other cylindrically-shaped member. In oneembodiment, the at least one thermal shunt member comprises at least oneextension member extending outwardly from a base member. In someembodiments, the at least one extension member comprises at least one ofa fin, a pin or a wing.

According to some embodiments, a system comprising a device inaccordance with the present application further comprises means forconnectivity to an electrophysiology recorder. In some embodiments, thesystem is configured to connect to an electrophysiology recorder. Insome embodiments, the system further comprises at least one of (i) agenerator for selectively energizing the device, and (ii) anelectrophysiology recorder.

According to some embodiments, an ablation device comprises an elongatebody (e.g., a catheter) having a distal end, an electrode (e.g., a RFelectrode, split-tip electrode, etc.) positioned at the distal end ofthe elongate body, at least one irrigation conduit extending at leastpartially through an interior of the elongate body, the at least oneirrigation conduit configured to place the electrode in fluidcommunication with a fluid source to selectively remove heat from theelectrode and/or tissue of a subject located adjacent the electrode andat least one heat transfer member placing the at least one irrigationconduit in thermal communication with a proximal portion of theelectrode to selectively remove heat from the proximal portion of theelectrode when the electrode is activated.

According to some embodiments, an ablation device comprises an elongatebody (e.g., a catheter, other medical instrument, etc.) comprising adistal end, an ablation member positioned at the distal end of theelongate body, at least one irrigation conduit extending at leastpartially through an interior of the elongate body, the at least oneirrigation conduit configured to place the ablation member in fluidcommunication with a fluid source and at least one thermal transfermember placing the at least one irrigation conduit in thermalcommunication with a proximal portion of the ablation member toselectively remove heat from the proximal portion of the ablation memberwhen the electrode is activated. In some embodiments, the ablationmember comprises a radiofrequency (RF) electrode, a microwave emitter,an ultrasound transducer, a cryoablation member and/or any other member.

According to some embodiments, the at least one thermal transfer membercomprises a thermal conductance greater than 300 W/m/° C. (e.g.,300-350, 350-400, 400-450, 450-500 W/m/° C., ranges between theforegoing, etc.). In other embodiments, the at least one thermaltransfer member comprises a thermal conductance greater than 500 W/m/°C. (e.g., 500-550, 550-600, 600-650, 650-700, 700-800, 800-900, 900-1000W/m/° C., ranges between the foregoing, greater than 1000 W/m/° C.,etc.).

According to some embodiments, the at least one thermal transfer membercomprises a diamond (e.g., industrial-grade diamond). In someembodiments, the at least one thermal transfer member comprises at leastone of a metal and an alloy (e.g., copper, beryllium, brass, etc.).

According to some embodiments, the electrode comprises a radiofrequency(RF) electrode. In one embodiment, the electrode comprises a split-tipelectrode. In some embodiments, the split-tip electrode comprises afirst electrode portion and at least a second electrode portion, whereinan electrically insulating gap is located between the first electrodeportion and the at least a second electrode portion to facilitatehigh-resolution mapping along a targeted anatomical area.

According to some embodiments, the device further comprises aradiometer. In some embodiments, the radiometer is located in thecatheter (e.g., at or near the electrode or other ablation member). Inother embodiments, however, the radiometer is located in the handle ofthe device and/or at another location of the device and/or accompanyingsystem. In embodiments of the device that comprise a radiometer, thecatheter comprises one or more antennas (e.g., at or near the electrode)configured to detect microwave signals emitted by tissue. In someembodiments, the device does not comprise a radiometer or does notincorporate radiometry technology (e.g., for measuring temperature oftissue). As discussed herein, other types of temperature-measurementdevices (e.g., thermocouples, thermistors, other temperature sensors,etc.) can be incorporate into a device or system.

According to some embodiments, an ablation device consists essentiallyof a catheter, an ablation member (e.g., a RF electrode, a split-tipelectrode, etc.), an irrigation conduit extending through an interior ofthe catheter to or near the ablation member, at least one electricalconductor (e.g., wire, cable, etc.) to selectively activate the ablationmember and at least one heat transfer member that places at least aportion of the ablation member (e.g., a proximal portion of the ablationmember) in thermal communication with the irrigation conduit.

According to some embodiments, an ablation device consists essentiallyof a catheter, an ablation member (e.g., a RF electrode, a split-tipelectrode, etc.), an irrigation conduit extending through an interior ofthe catheter to or near the ablation member, at least one electricalconductor (e.g., wire, cable, etc.) to selectively activate the ablationmember, an antenna configured to receive microwave signals emitted bytissue of a subject, a radiometer and at least one heat transfer memberthat places at least a portion of the ablation member (e.g., a proximalportion of the ablation member) in thermal communication with theirrigation conduit.

According to some embodiments, the at least one irrigation conduit is indirect thermal communication with the at least one thermal transfermember. In some embodiments, the at least one irrigation conduit is notin direct thermal communication with the at least one thermal transfermember. In some embodiments, the irrigation conduit is fluidcommunication only with exit ports located along the distal end of theelongate body. In some embodiments, the catheter only comprisesirrigation exit openings along a distal end of the catheter (e.g., alonga distal end or the electrode). In some embodiments, the system does notcomprise any irrigation openings along the heat transfer members.

According to some embodiments, the at least one irrigation conduitdirectly contacts the at least one thermal transfer member. In someembodiments, the at least one irrigation conduit does not contact the atleast one thermal transfer member. In one embodiment, at least a portionof the heat transfer member extends to an exterior of the catheteradjacent the proximal end of the electrode. In some embodiments, atleast a portion of the heat transfer member extends proximally to theproximal end of the electrode. In certain embodiments, at least aportion of the heat transfer member extends distally to the proximal endof the electrode such that at least a portion of the heat transfermember is located along a length of the electrode. According to someembodiments, the at least one irrigation conduit comprises a metallicmaterial and/or other thermally conductive materials.

According to some embodiments, the heat transfer member comprises a diskor other cylindrically-shaped member. In some embodiments, the heattransfer member comprises at least one extension member extendingoutwardly from a base member.

According to some embodiments, the device further comprises a radiometerto enable the device and/or accompanying system to detect a temperatureto tissue of the subject at a depth. In some embodiments, the radiometeris included, at least in part, in the catheter. In other embodiments,the radiometer is located, at least in part, in the handle of the systemand/or in a portion of the device and/or accompanying system external tothe catheter.

According to some embodiments, a method of heat removal from an ablationmember during an ablation procedure comprises activating an ablationsystem, the system comprising an elongate body comprising a distal end,an ablation member positioned at the distal end of the elongate body, atleast one irrigation conduit extending at least partially through aninterior of the elongate body, and at least one thermal transfer member,wherein the at least one irrigation conduit configured to place theablation member in fluid communication with a fluid source toselectively remove heat from the ablation member and/or tissue of asubject located adjacent the ablation member, and delivering fluidthrough the at least one irrigation conduit, wherein the at least onethermal transfer member places the at least one irrigation conduit inthermal communication with a proximal portion of the ablation member toselectively remove heat from the proximal portion of the ablation memberwhen the electrode is activated.

According to some embodiments, the elongate body is advanced to a targetanatomical location of the subject through a bodily lumen of thesubject. In some embodiments, the bodily lumen of the subject comprisesa blood vessel, an airway or another lumen of the respiratory tract, alumen of the digestive tract, a urinary lumen or another bodily lumen.

According to some embodiments, the ablation member comprises aradiofrequency (RF) electrode, a microwave emitter, an ultrasoundtransducer, a cryoablation member and/or the like. In some embodiments,the at least one thermal transfer member comprises a thermal conductancegreater than 300 W/m/° C. In one embodiment, the at least one thermaltransfer member comprises a thermal conductance greater than 500 W/m/°C.

According to some embodiments, the at least one thermal transfer membercomprises a diamond (e.g., industrial-grade diamond). In someembodiments, the at least one thermal transfer member comprises at leastone of a metal and an alloy (e.g., copper, beryllium, brass, etc.).

According to some embodiments, a system comprises an ablation deviceaccording to any of the embodiments disclosed herein. In someembodiments, the system additionally comprises means for connectivity toan electrophysiology recorder. In some embodiments, the system isconfigured to connect to an electrophysiology recorder. In someembodiments, the system further comprises at least one of (i) agenerator for selectively energizing the device, and (ii) anelectrophysiology recorder.

According to one embodiment, a medical instrument (for example, ablationcatheter) includes an elongate body having a proximal end and a distalend. The medical instrument also includes an energy delivery memberpositioned at the distal end of the elongate body that is configured todeliver energy to the targeted tissue. The medical instrument furtherincludes a first plurality of temperature-measurement devices positionedwithin the energy delivery member and being thermally insulated from theenergy delivery member and a second plurality of temperature-measurementdevices positioned along the elongate body and spaced apart axially fromthe first plurality of temperature-measurement devices, the secondplurality of temperature-measurement devices also being thermallyinsulated from the energy delivery member. The energy delivery membermay optionally be configured to contact the tissue. The first pluralityof temperature-measurement devices may optionally be positioned along afirst plane that is substantially perpendicular to a longitudinal axisof the elongate body. The second plurality of temperature-measurementdevices may optionally be positioned along a second plane that issubstantially perpendicular to a longitudinal axis of the elongate bodyand spaced apart axially along the longitudinal axis proximal to thefirst plane. The energy delivery member may optionally comprise one ormore electrode portions, one or more ultrasound transducers, one or morelaser elements, or one or more microwave emitters.

According to one embodiment, a medical instrument (for example, anablation catheter or other device) comprises an elongate body having aproximal end and a distal end. The medical instrument comprises at leastone energy delivery member (for example, a tip electrode or multipleelectrode portions) positioned at the distal end of the elongate body.In this embodiment, the at least one energy delivery member isconfigured to deliver energy (for example, radiofrequency energy,acoustic energy, microwave power, laser energy) to the targeted tissuewith or without contacting the tissue. In one embodiment, the energy issufficient to generate a lesion at a depth from a surface of thetargeted tissue. The embodiment of the medical instrument comprises afirst plurality of temperature-measurement devices carried by, orpositioned within separate apertures, recesses or other openings formedin a distal end (for example, a distal-most surface) of the at least oneenergy delivery member. The first plurality of temperature-measurementdevices are thermally insulated from the energy delivery member. Theembodiment of the medical instrument comprises a second plurality oftemperature-measurement devices positioned adjacent to (for example,within 1 mm of) a proximal end of the at least one energy deliverymember (for example, carried by or within the energy delivery member orcarried by or within the elongate body proximal of the proximal end ofthe energy delivery member), the second plurality oftemperature-measurement devices being thermally insulated from the atleast one energy delivery member. The second plurality oftemperature-measurement devices may be positioned just proximal or justdistal of the proximal end of the at least one energy delivery member.If the medical instrument comprises two or more energy delivery members,then the second plurality of temperature-measurement devices may bepositioned adjacent the proximal edge of the proximal-most energydelivery member and the first plurality of temperature-measurementdevices may be positioned within the distal-most energy delivery member.In some embodiments, the second plurality of temperature-measurementdevices are positioned along a thermal shunt member (for example,thermal transfer member) proximal of the at least one energy deliverymember. In some embodiments, the second plurality oftemperature-measurement devices is positioned along a plane that isperpendicular or substantially perpendicular to a longitudinal axis ofthe distal end of the elongate body and spaced proximal to the firstplurality of temperature-measurement devices.

In some embodiments, each of the temperature-measurement devicescomprises a thermocouple or a thermistor (for example, Type K or Type Tthermocouples). In some embodiments, the first plurality oftemperature-measurement devices comprises at least threetemperature-measurement devices and the second plurality oftemperature-measurement devices comprises at least threetemperature-measurement devices. In one embodiment, the first pluralityof temperature-measurement devices consists of only threetemperature-measurement devices and the second plurality oftemperature-measurement devices consists of only threetemperature-measurement devices. Each of the first plurality oftemperature-measurement devices and each of the second plurality oftemperature-measurement devices may be spaced apart (equidistantly ornon-equally spaced) from each of the other temperature-measurementdevices of its respective group (for example, circumferentially orradially around an outer surface of the elongate body or otherwisearranged). For example, where three temperature-measurement devices areincluded in each plurality, group or set, the temperature-measurementdevices may be spaced apart by about 120 degrees. In some embodiments,the first plurality of temperature-measurement devices and the secondplurality of temperature-measurement devices protrude or otherwiseextend beyond an outer surface of the elongate body to facilitateincreased depth of insertion (for example, burying) within the targetedtissue. In one embodiment the elongate body is cylindrical orsubstantially cylindrical. The distal ends of thetemperature-measurement devices may comprise a generally rounded casingor shell to reduce the likelihood of penetration or scraping of thetargeted tissue.

In accordance with one embodiment, a medical instrument (for example,ablation device) comprises an elongate body having a proximal end and adistal end and a split-tip electrode assembly positioned at the distalend of the elongate body. The split-tip electrode assembly comprises afirst electrode member positioned at a distal terminus of the distal endof the elongate body, a second electrode member positioned proximal tothe first electrode member and spaced apart from the first electrodemember, and an electrically-insulating gap between the first electrodemember and the second electrode member. The first electrode member andthe second electrode member may be configured to contact tissue of asubject and to deliver radiofrequency energy to the tissue. In someembodiments, the energy may be sufficient to ablate the tissue. Theelectrically-insulating gap may comprise a gap width separating thefirst electrode member and the second electrode member. The embodimentof the medical instrument comprises a first plurality of temperaturesensors positioned within separate openings, apertures, slits, slots,grooves or bores formed in the first electrode member and spaced apart(for example, circumferentially, radially or otherwise) and a secondplurality of temperature sensors positioned at a region proximal to thesecond electrode member (for example, adjacent to (just proximal or justdistal, within less than 1 mm from) a proximal edge of the secondelectrode member). The second plurality of temperature sensors arethermally insulated from the second electrode member. In someembodiments, the second plurality of temperature sensors is spaced apartcircumferentially or radially around an outer circumferential surface ofthe elongate body. The first plurality of temperature sensors may bethermally insulated from the first electrode member and may extendbeyond an outer surface (for example, distal-most surface) of the firstelectrode member. In one embodiment, at least a portion of each of thesecond plurality of temperature sensors extends beyond the outercircumferential surface of the elongate body.

In some embodiments, the medical instrument comprises a heat exchangechamber (for example, irrigation conduit) extending at least partiallythrough an interior of the elongate body. The medical instrument may becoupled to a fluid source configured to supply cooling fluid to the heatexchange chamber and a pump configured to control delivery of thecooling fluid to the heat exchange chamber from the fluid source throughone or more internal lumens within the heat exchange chamber. In oneembodiment, the first electrode member comprises a plurality ofirrigation exit ports in fluid communication with the heat exchangechamber such that the cooling fluid supplied by the fluid source exitsfrom the irrigation exit ports, thereby providing cooling to thesplit-tip electrode assembly, blood and/or tissue being heated.

For open irrigation arrangements, the medical instrument (for example,ablation device) may comprise a fluid delivery lumen having a diameteror other cross-sectional dimension smaller than the lumen of the heatexchange chamber (for example, irrigation conduit) to facilitateincreased velocity to expel the saline or other fluid out of theirrigation exit ports at a regular flow rate. For closed irrigationarrangements, the medical instrument may comprise an inlet lumen (forexample, fluid delivery lumen) extending between the heat exchangechamber and the fluid source and an outlet lumen (for example, returnlumen) extending between the heat exchange chamber (for example,irrigation conduit) and a return reservoir external to the medicalinstrument. In one embodiment, a distal end (for example, outlet) of theinlet lumen is spaced distally from the distal end (for example, inlet)of the outlet lumen so as to induce turbulence or other circulationwithin the heat exchange chamber. In various embodiments, an irrigationflow rate is 10 mL/min or less (for example, 9 mL/min or less, 8 mL/minor less, 7 mL/min or less, 6 mL/min or less, 5 m/min or less). In someembodiments, the medical instruments are not irrigated.

According to one embodiment, a medical instrument (for example, ablationdevice) comprises an elongate body (for example, a catheter, wire,probe, etc.) comprising a proximal end and a distal end and alongitudinal axis extending from the proximal end to the distal end. Themedical instrument comprises a split-tip electrode assembly. In theembodiment, the split-tip electrode assembly comprises a first electrodemember positioned at a distal terminus of the distal end of the elongatebody and a second electrode member positioned proximal to the firstelectrode member and spaced apart from the first electrode member. Thefirst electrode member and the second electrode member are configured tocontact tissue of a subject and to deliver radiofrequency energy to thetissue. The energy delivered may be sufficient to at least partiallyablate or otherwise heat the tissue. The split-tip electrode assemblyalso comprises an electrically-insulating gap comprising a gap widthseparating the first electrode member and the second electrode member.The embodiment of the ablation device further comprises at least onethermal transfer member in thermal communication with the first andsecond electrode members to selectively remove or dissipate heat fromthe first and second electrode members, a first plurality oftemperature-measurement devices positioned within the first electrodemember and spaced apart (for example, circumferentially, radially) and asecond plurality of temperature-measurement devices positioned within aportion of the at least one thermal heat shunt member (for example, heattransfer member) proximal to the second electrode member. The firstplurality of temperature-measurement devices is thermally insulated fromthe first electrode member and may extend beyond an outer surface of thefirst electrode member in a direction that is at least substantiallyparallel to the longitudinal axis of the elongate body. The secondplurality of thermocouples is thermally insulated from the secondelectrode member and may extend beyond an outer surface of the at leastone thermal heat shunt member in a direction that is at leastsubstantially perpendicular to the longitudinal axis of the elongatebody.

In some embodiments, the medical instrument comprises a heat exchangechamber (for example, irrigation conduit) extending at least partiallythrough an interior of the elongate body. The medical instrument may befluidly coupled to a fluid source configured to supply cooling fluid tothe heat exchange chamber and a pump configured to control delivery ofthe cooling fluid. In one embodiment, the first electrode membercomprises a plurality of irrigation exit ports in fluid communicationwith the heat exchange chamber such that the cooling fluid supplied bythe fluid source is expelled from the irrigation exit ports, therebyproviding cooling to the split-tip electrode assembly. In someembodiments, at least an inner surface or layer of the heat exchangechamber comprises a biocompatible material, such as stainless steel.

In some embodiments, the at least one thermal shunt member (for example,heat shunt network or heat transfer member(s)) comprises a thermalconductance greater than 300 W/m/° C. (for example, 300-350, 350-400,400-450, 450-500 W/m/° C., ranges between the foregoing, etc.). In otherembodiments, the at least one thermal transfer member comprises athermal conductance greater than 500 W/m/° C. (for example, 500-550,550-600, 600-650, 650-700, 700-800, 800-900, 900-1000 W/m/° C., rangesbetween the foregoing, greater than 1000 W/m/° C., etc.). According tosome embodiments, the at least one thermal transfer member comprises adiamond (for example, industrial-grade diamond).

The electrode member(s) may comprise platinum in any of the embodiments.The temperature-measurement devices may comprise one of more of thefollowing types of thermocouples: nickel alloy, platinum/rhodium alloy,tungsten/rhenium alloy, gold/iron alloy, noble metal alloy,platinum/molybdenum alloy, iridium/rhodium alloy, pure noble metal, TypeK, Type T, Type E, Type J, Type M, Type N, Type B, Type R, Type S, TypeC, Type D, Type G, and/or Type P.

According to some embodiments, the medical instrument comprises at leastone separator positioned within the at least one electrically-insulatinggap. In one embodiment, the at least one separator comprises a portionof the at least one thermal transfer member. For example, the at leastone separator may comprise industrial grade diamond.

According to some embodiments, the medical instrument comprises at leastone conductor configured to conduct current from an energy source to thesplit-tip electrode assembly or other ablation members. In someembodiments, the first plurality of thermocouples or othertemperature-measurement devices and the second plurality ofthermocouples or other temperature-measurement devices extend up to 1 mmbeyond the outer surface of the first electrode member and the at leastone thermal transfer member, respectively.

According to some embodiments, an outer diameter of a portion of the atleast one thermal heat transfer member comprising the second pluralityof temperature-measurement devices is greater than the outer diameter ofthe elongate body so as to facilitate greater insertion depth within thetissue, thereby increasing isolation of the thermocouples or othertemperature-measurement devices from the thermal effects of theelectrode member(s).

In accordance with several embodiments, a treatment system comprises amedical instrument (for example, an ablation catheter), a processor, andan energy source. The medical instrument comprises an elongate bodyhaving a proximal end and a distal end, an energy delivery member (forexample, electrode) positioned at the distal end of the elongate body, afirst plurality of temperature-measurement devices carried by orpositioned along or within the energy delivery member, and a secondplurality of temperature-measurement devices positioned proximal of theelectrode along the elongate body. The energy delivery member may beconfigured to contact tissue of a subject and to deliver energygenerated by the energy source to the tissue. In some embodiments, theenergy is sufficient to at least partially ablate the tissue. In someembodiments, the first plurality of temperature-measurement devices arethermally insulated from the energy delivery member and the secondplurality of temperature-measurement devices are thermally insulatedfrom the energy delivery member. In one embodiment, the second pluralityof temperature-measurement devices is spaced apart around an outersurface of the elongate body. The energy source of the embodiment of thesystem may be configured to provide the energy to the energy deliverymember through one or more conductors (for example, wires, cables, etc.)extending from the energy source to the energy delivery member.

The processor of the embodiment of the system may be programmed orotherwise configured (for example, by execution of instructions storedon a non-transitory computer-readable storage medium) to receive signalsfrom each of the temperature-measurement devices indicative oftemperature and determine an orientation of the distal end of theelongate body of the ablation catheter with respect to the tissue basedon the received signals. In some embodiments, the processor may beconfigured to adjust one or more treatment parameters based on thedetermined orientation. The one or more treatment parameters mayinclude, among other things, duration of treatment, power of energy,target or setpoint temperature, and maximum temperature.

In some embodiments, the processor is configured to cause anidentification of the determined orientation to be output to a display.The output may comprise textual information (such as a word, phrase,letter or number). In some embodiments, the display comprises agraphical user interface and the output comprises one or more graphicalimages indicative of the determined orientation.

In some embodiments, the determination of the orientation of the distalend of the elongate body of the medical instrument with respect to thetissue is based on a comparison of tissue measurements determined fromreceived signals with respect to each other. The orientation may beselected from one of three orientation options: perpendicular, paralleland angled or oblique. In one embodiment, the processor is configured togenerate an output to terminate delivery of energy if the determinedorientation changes during energy delivery (for example, an alarm tocause a user to manually terminate energy delivery or a signal toautomatically cause termination of energy delivery).

According to some embodiments, a treatment system comprises a medicalinstrument (for example, an ablation catheter) and a processor. Themedical instrument may comprise an elongate body having a proximal endand a distal end, an energy delivery member positioned at the distal endof the elongate body, the energy delivery member being configured tocontact tissue of a subject and to deliver energy (for example, ablativeenergy) to the tissue, a first plurality of temperature-measurementdevices positioned within the energy delivery member, and a secondplurality of temperature-measurement devices positioned proximal to theenergy delivery member along the elongate body. The first plurality oftemperature-measurement devices may be thermally insulated from theenergy delivery member and may be spaced apart from each other and thesecond plurality of temperature-measurement devices may be thermallyinsulated from the energy delivery member and may be spaced apart aroundan outer surface of the elongate body.

A processor of the embodiment of the treatment system may be programmedor otherwise configured (for example, by execution of instructionsstored on a non-transitory computer-readable storage medium) to receivesignals from each of the temperature-measurement devices, and calculatea peak temperature of the tissue at a depth based on the receivedsignals. The peak temperature may comprise an extreme temperature (forexample, a peak or a valley/trough temperature, a hot or a coldtemperature, a positive peak or a negative peak).

According to some embodiments, the processor is configured to calculatethe peak temperature of the tissue at a depth by comparing individualtemperature measurements determined from the received signals to eachother. In some embodiments, the processor is configured to adjust one ormore treatment parameters based on the calculated peak temperature,including duration of treatment, power of energy, target temperature,and maximum temperature.

According to some embodiments, the processor is configured to generatean output to automatically terminate delivery of energy if thecalculated peak temperature exceeds a threshold temperature or togenerate an alert to cause a user to manually terminate energy delivery.In some embodiments, the processor is configured to cause anidentification of the calculated peak temperature to be output to adisplay (for example, using a color, textual information, and/ornumerical information).

In accordance with several embodiments, a treatment system comprises amedical instrument (for example, ablation catheter) comprising anelongate body comprising a proximal end and a distal end, an energydelivery member positioned at the distal end of the elongate body. Inone embodiment, the energy delivery member (for example, electrode) isconfigured to contact tissue of a subject and to deliver energy (forexample, ablative energy) to the tissue. The medical instrumentcomprises a first plurality of temperature-measurement devicespositioned within separate openings or apertures formed in the energydelivery member, and a second plurality of temperature-measurementdevices positioned proximal to the energy delivery member along theelongate body. The first plurality of temperature-measurement devicesmay be thermally insulated from the electrode and spaced apart from eachother and the second plurality of temperature-measurement devices may bethermally insulated from the electrode. In one embodiment, the secondplurality of temperature-measurement devices is spaced apart around anouter surface of the elongate body. The treatment system may alsocomprise a processor that is programmed or otherwise configured (forexample, by execution of instructions stored on a non-transitorycomputer-readable storage medium) to receive signals from each of thetemperature-measurement devices and determine an estimated location of apeak temperature zone at a depth within the tissue based, at least inpart, on the received signals. In some embodiments, the processordetermines individual temperature measurements based on the receivedsignals and compares them to determine the estimated location of thepeak temperature. The processor may be configured to adjust one or moretreatment parameters based on the estimated location, includingduration, power, target temperature, and maximum temperature. Theprocessor may also be configured to cause an identification of theestimated location to be output to a display. The output may comprisealphanumeric information and/or one or more graphical images indicativeof the estimated location of the peak temperature zone.

In accordance with several embodiments, a method of determining a peaktemperature of tissue being ablated at a depth from a surface of thetissue may comprise receiving signals indicative of temperature from afirst plurality of temperature sensors positioned at a distal end of anablation catheter. In one embodiment, each of the first plurality oftemperature sensors is spaced apart around the distal end of theablation catheter. The method also comprises receiving signalsindicative of temperature from a second plurality of temperature sensorspositioned at a distance proximal to the first plurality of temperaturesensors. The method further comprises determining temperaturemeasurements from the signals received from the first plurality oftemperature sensors and the second plurality of temperature sensors andcomparing the determined temperature measurements to each other. In someembodiments, the method comprises applying one or more correctionfactors to one or more of the determined temperature measurements based,at least in part, on the comparison to determine the peak temperature.In one embodiment, the method comprises outputting the determined peaktemperature on a display textually, visually and/or graphically. In oneembodiment, the method comprises adjusting one or more treatment (forexample, ablation) parameters and/or terminating ablation based on thedetermined hotspot temperature. The second plurality of temperaturesensors may be spaced apart around a circumference of the ablationcatheter or other medical instrument.

According to some embodiments, a method of determining a location of apeak temperature zone within tissue being ablated comprises receivingsignals indicative of temperature from a first plurality of temperaturesensors positioned at a distal end of an ablation catheter. In oneembodiment, each of the first plurality of temperature sensors arespaced apart around the distal end of the ablation catheter. The methodcomprises receiving signals indicative of temperature from a secondplurality of temperature sensors positioned at a distance proximal tothe first plurality of temperature sensors. The method further comprisesdetermining temperature measurements from the signals received from thefirst plurality of temperature sensors and the second plurality oftemperature sensors and, comparing the determined temperaturemeasurements to each other. The method may comprise determining alocation of a peak temperature zone of a thermal lesion based, at leastin part, on the comparison. In one embodiment, the method comprisesoutputting the determined peak location on a display, textually,visually and/or graphically. In one embodiment, each of the secondplurality of temperature sensors is spaced apart around a circumferenceof the ablation catheter.

According to some embodiments, a method of determining an orientation ofa distal tip of an ablation catheter with respect to tissue in contactwith the distal tip comprises receiving signals indicative oftemperature from a first plurality of temperature sensors positioned ata distal end of an ablation catheter and receiving signals indicative oftemperature from a second plurality of temperature sensors positioned ata distance proximal to the first plurality of temperature sensors. Themethod further comprises determining temperature measurements from thesignals received from the first plurality of temperature sensors and thesecond plurality of temperature sensors and comparing each of thedetermined temperature measurements with each other. The method furthercomprises determining an orientation of a distal tip of an ablationcatheter with respect to tissue in contact with the distal tip based, atleast in part, on the comparison. In one embodiment, the methodcomprises outputting the determined orientation on a display. The outputmay comprise textual information or one or more graphical images. Theembodiments of the methods may also comprise terminating energy deliveryor generating an output (for example, an alert) to signal to a user thatenergy delivery should be terminated. In some embodiments, each of thefirst plurality of temperature sensors is spaced apart around a distalend of the ablation catheter and each of the second plurality oftemperature sensors is spaced apart around a circumference of theablation catheter.

In accordance with several embodiments, a system comprises at least onesignal source configured to deliver at least a first frequency and asecond frequency to a pair of electrodes or electrode portions of acombination electrode or electrode assembly. The system also comprises aprocessing device configured to: obtain impedance measurements while thefirst frequency and the second frequency are being applied to the pairof electrodes by the signal source, process the electrical (for example,voltage, current, impedance) measurements obtained at the firstfrequency and the second frequency, and determine whether the pair ofelectrodes is in contact with tissue based on said processing of theelectrical (for example, impedance) measurements. The pair of electrodesmay be positioned along a medical instrument (for example, at a distalend portion of an ablation catheter). The pair of electrodes maycomprise radiofrequency electrodes and the at least one signal sourcemay comprise one, two or more sources of radiofrequency energy.

The signal source may comprise a first signal source configured togenerate, deliver or apply signals to the pair of electrodes having afrequency configured for tissue ablation and a second signal sourceconfigured to generate, deliver or apply signals to the pair ofelectrodes having frequencies adapted for contact sensing and/or tissuetype determination (for example, whether the tissue is ablated or stillviable). The first and second signal sources may be integrated within anenergy delivery module (for example, RF generator) or within an elongatebody or handle of a medical instrument (for example, ablation catheter).In some embodiments, the second signal source is within a contactsensing subsystem, which may be a distinct and separate component fromthe energy delivery module and medical instrument or integrated withinthe energy delivery module or medical instrument. In one embodiment,only one signal source capable of applying signals having frequenciesadapted for ablation or other treatment and signals having frequenciesadapted for contact sensing or tissue type determination functions isused. The frequencies adapted for contact sensing or tissue typedetermination may be within the treatment frequency range or outside thetreatment frequency range. By way of example, in one non-limitingembodiment, the system comprises an energy source configured togenerate, deliver or apply signals to at least a pair of electrodemembers (and also to a ground pad or reference electrode) to deliverenergy having a frequency configured for tissue ablation or othertreatment and a signal source configured to generate, deliver or applysignals to the pair of electrode members (and not to a ground pad orreference electrode) having frequencies adapted for contact sensingand/or tissue type determination (for example, whether the tissue isablated or still viable). The energy source and the signal source mayboth be integrated within an energy delivery module (for example, RFgenerator) or one of the sources (for example, the signal source) may beincorporated within an elongate body or handle of a medical instrument(for example, ablation catheter). In some embodiments, the signal sourceis within a contact sensing subsystem, which may be a distinct andseparate component from the energy delivery module and medicalinstrument or integrated within the energy delivery module or medicalinstrument. In some embodiments, a single source configured for applyingsignals having frequencies adapted for ablation or other treatment andconfigured for applying signals having frequencies adapted for contactsensing or tissue type determination functions is used. Signals havingthe treatment frequencies may also be delivered to a ground pad orreference electrode.

In some embodiments, the system consists essentially of or comprises amedical instrument (for example, an energy delivery device), one or moreenergy sources, one or more signal sources and one or more processingdevices. The medical instrument (for example, energy delivery catheter)may comprise an elongate body having a proximal end and a distal end anda pair of electrodes or electrode portions (for example, a combination,or split-tip, electrode assembly) positioned at the distal end of theelongate body. In one embodiment, the pair of electrodes comprises afirst electrode positioned on the elongate body and a second electrodepositioned adjacent (for example, proximal of) the first electrode. Thefirst electrode and the second electrode may be configured to contacttissue of a subject and provide energy to the tissue to heat (forexample, ablate or otherwise treat) the tissue at a depth from thesurface of the tissue. In one embodiment, the pair of electrodescomprises an electrically insulating gap positioned between the firstelectrode and the second electrode, the electrically insulating gapcomprising a gap width separating the first and second electrodes. Aseparator (for example, a capacitor or insulation material) may bepositioned within the electrically insulating gap.

The one or more signal sources may be configured to deliver signals overa range of frequencies (for example, frequencies within a radiofrequencyrange). In some embodiments, the processing device is configured toexecute specific program instructions stored on a non-transitorycomputer-readable storage medium to: obtain impedance or otherelectrical measurements while different frequencies of energy within therange of frequencies are being applied to the pair of electrodes by asignal source, process the impedance or other electrical measurementsobtained at the first frequency and the second frequency, and determinewhether at least one of (for example, the distal-most electrode) thepair of electrodes is in contact with tissue based on said processing ofthe impedance or other electrical measurements.

In some embodiments, the medical instrument consists essentially of orcomprises a radiofrequency ablation catheter and the first and secondelectrodes or electrode portions comprise radiofrequency electrodes. Thesignal source(s) may comprise a radiofrequency (RF) generator. In oneembodiment, the range of frequencies that is delivered by the signalsource(s) (for example, of a contact sensing subsystem) comprises atleast a range between 1 kHz and 5 MHz (for example, between 5 kHz and1000 kHz, between 10 kHz and 500 kHz, between 5 kHz and 800 kHz, between20 kHz and 800 kHz, between 50 kHz and 5 MHz, between 100 kHz and 1000kHz, and overlapping ranges thereof). The signal source(s) may also beconfigured to deliver frequencies below and above this range. Thefrequencies may be at least greater than five times or at least greaterthan ten times the electrogram mapping frequencies so as not tointerfere with high-resolution mapping images or functions obtained bythe first and second electrodes or electrode portions. In oneembodiment, the different frequencies at which impedance measurementsare obtained consists only of two discrete frequencies. In anotherembodiment, the different frequencies comprise two or more discretefrequencies. In some embodiments, the processing device is configured toobtain impedance measurements while a full sweep of frequencies from aminimum frequency to a maximum frequency of the range of frequencies isapplied to the pair of electrodes or electrode portions. As one example,the range of frequencies is between 5 kHz and 1000 kHz. The secondfrequency may be different from (for example, higher or lower than) thefirst frequency.

The system may comprise an ablative energy source (for example, signalsource such as an RF generator) configured to deliver signals to thepair of electrodes (and possibly also to a ground pad or referenceelectrode) to generate energy sufficient to ablate or otherwise treattissue (such as cardiac tissue). In one embodiment, the processingdevice is configured to adjust one or more energy delivery parameters ofthe ablative energy based on a determination of whether at least one ofthe pair of electrodes is in contact with tissue and/or is configured toterminate energy delivery based on a determination of whether at leastone of the pair of electrodes is in contact with tissue or that contacthas been lost. In some embodiments, the ablative energy source and theat least one signal source comprise a single source. In otherembodiments, the signal source comprises a first source and the ablativeenergy source comprises a second source that is separate and distinctfrom the first source. In some embodiments, the processing is performedin the time domain. In some embodiments, the processing is performed inthe frequency domain. Portions of the processing may be performed inboth the time domain and the frequency domain.

In some embodiments, the processing device is configured to executespecific program instructions stored on a non-transitorycomputer-readable storage medium to generate an output indicative ofcontact. The processing device may be configured to cause the generatedoutput to be displayed on a display (for example an LCD or LED monitor)in communication with the processing device. In various embodiments, theoutput comprises textual information, quantitative information (forexample, numeric information, binary assessment of whether contactexists or not) and/or a qualitative information (for example, color orother information indicative of a level of contact).

In accordance with several embodiments, a system comprises a signalsource configured to deliver signals having a range of frequencies and aprocessing device configured to execute specific program instructionsstored on a non-transitory computer-readable storage medium to: obtainimpedance or other electrical measurements while different frequenciesof energy are being applied to a pair of electrodes (for example,combination electrode, or split-tip, electrode assembly) by the signalsource, compare the impedance measurements obtained at the differentfrequencies of energy; and determine whether or not tissue in contactwith at least one of the pair of electrodes has been ablated. In someembodiments, the range of frequencies over which contact determinationis made is between 5 kHz and 1000 kHz. The different frequencies consistof two discrete frequencies in one embodiment or may comprise two ormore discrete frequencies in other embodiments. The processing devicemay be configured to obtain impedance measurements while a full sweep offrequencies from a minimum frequency to a maximum frequency of the rangeof frequencies (for example, 5 kHz to 1000 kHz) is applied to the pairof electrodes. In some embodiments, one component of an impedancemeasurement (for example, impedance magnitude) is obtained at a firstfrequency and a second component of a different impedance measurement(for example, phase angle) is obtained at a second frequency. Acomparison (for example, derivative of impedance versus frequency, deltaor slope of impedance vs. frequency) of impedance magnitude measurementsat two or more different frequencies may also be obtained. A weightedcombination of various impedance measurements at two or more differentfrequencies may be calculated by the processing device and used by theprocessing device to determine an overall contact level or state. Theimpedance measurements may be obtained directly or may be calculatedbased on electrical parameter measurements, such as voltage and/orcurrent measurements.

In some embodiments, the processing device is configured to executespecific program instructions stored on a non-transitorycomputer-readable storage medium to generate an output indicative oftissue type based on the determination of whether or not tissue incontact with at least one of the pair of electrodes has been ablated.The processing device may be configured to cause the generated output tobe displayed on a display in communication with the processing device.The output may comprise one or more of textual information, a color orother qualitative information, and numerical information. In variousembodiments, the processing device is configured to adjust one or moreenergy delivery parameters based on the determination of whether thetissue in contact with the pair of electrodes has been ablated and/or isconfigured to terminate energy delivery based on the determination ofwhether tissue in contact with the pair of electrodes has been ablated.

In accordance with several embodiments, a system for determining whethera medical instrument is in contact with tissue based, at least in part,on impedance measurements comprises a signal source configured todeliver signals having different frequencies to a pair of electrodes ofa medical instrument and a processing device configured to process aresulting waveform that formulates across the pair of electrodes toobtain impedance measurements at a first frequency and a secondfrequency and determine a ratio between the magnitude of the impedanceat the second frequency and the first frequency. If the determined ratiois below a predetermined threshold indicative of contact, the processingdevice is configured, upon execution of stored instructions on acomputer-readable medium, to generate a first output indicative ofcontact. If the determined ratio is above the predetermined threshold,the processing device is configured to, upon execution of storedinstructions on a computer-readable medium, generate a second outputindicative of no contact. In one embodiment, the signal source comprisesa radiofrequency energy source. The first and second frequencies may bebetween 5 kHz and 1000 kHz. In some embodiments, the signal source isconfigured to generate signals having a frequency adapted for tissueablation. In other embodiments, the system comprises a second signalsource (or an ablative energy source) configured to generate signalshaving a frequency adapted for tissue ablation. The frequency adaptedfor tissue ablation may be between 400 kHz and 600 kHz (for example, 400kHz, 450 kHz, 460 kHz, 480 kHz, 500 kHz, 550 kHz, 600 KHz, 400 KHZ-500kHz, 450 kHz-550 kHz, 500 kHz-600 kHz, or overlapping ranges thereof).In various embodiments, the predetermined threshold is a value between0.5 and 0.9. Processing the waveforms may comprise obtaining voltageand/or current measurements and calculating impedance measurements basedon the voltage and/or current measurements or directly obtainingimpedance measurements.

A method of determining whether a medical instrument is in contact witha target region (for example, tissue) based, at least in part, onelectrical measurements (for example, impedance measurements), maycomprise applying signals having a first frequency and a secondfrequency to a pair of electrodes or electrode portions of the medicalinstrument, processing a resulting waveform to obtain impedancemeasurements at the first frequency and the second frequency, anddetermining a ratio between the magnitude of the impedance at the secondfrequency and the first frequency. If the determined ratio is below apredetermined threshold indicative of contact, the method comprisesgenerating a first output indicative of contact. If the determined ratiois above the predetermined threshold, the method comprises generating asecond output indicative of no contact.

In accordance with several embodiments, a system for determining acontact state of a distal end portion of a medical instrument with atarget region (for example, tissue) based, at least in part, onelectrical measurements comprises a signal source configured to generateat least one signal having a first frequency and a second frequency tobe applied to a pair of electrode members of a combination electrodeassembly. The signal source may be a component of a contact sensing ordetection subsystem or an energy delivery module, such as aradiofrequency generator. The system also comprises a processor or othercomputing device configured to, upon execution of specific programinstructions stored in memory or a non-transitory computer-readablestorage medium, cause the signal source to generate and apply the atleast one signal to the pair of electrode members. The signal may be asingle multi-tone waveform or signal or multiple waveforms or signalshaving a single frequency.

The processor may be configured to process a resulting waveform thatformulates across the pair of electrode members to obtain a firstelectrical measurement at the first frequency and to process theresulting waveform that formulates across the pair of electrode membersto obtain a second electrical measurement at the second frequency of theplurality of frequencies. The processor is further configured to:determine an impedance magnitude based on the first electricalmeasurement (for example, voltage and/or current measurement), determinean impedance magnitude and a phase based on the second electricalmeasurement, and calculate a contact indication value indicative of astate of contact between the distal end portion of the medicalinstrument and the target region based on a criterion combining theimpedance magnitude based on the first electrical measurement, a ratioof the impedance magnitudes based on the first electrical measurementand the second electrical measurement, and the phase based on the secondelectrical measurement. The first and second electrical measurements maycomprise voltage and/or current measurements or direct impedancemeasurements between the pair of electrode members. In some embodiments,the first and second electrical measurements do not comprise directmeasurements of electrical parameters between an electrode and tissuebut are measurements between two electrode members. Impedancemeasurements may be calculated based on the voltage and/or currentmeasurements.

In some embodiments, the criterion comprises a weighted combination ofthe impedance magnitude based on the first electrical measurement, aratio of the impedance magnitudes based on the first and secondelectrical measurements, and the phase based on the second electricalmeasurement. In some embodiments, the criterion comprises an if-thencase conditional criterion, such as described in connection with FIGS.11 and 11A. In various embodiments, only one impedance measurement orcalculation (for example, only impedance magnitude, only slope betweenimpedance magnitude values, or only phase) or only two types ofimpedance measurements or calculations are used to determine the contactstate.

In accordance with several embodiments, a system for determining whethera medical instrument is in contact with a target region (for example,tissue) based, at least in part, on impedance measurements consistsessentially of or comprises a signal source configured to generate oneor more signals having a first frequency and a second frequency to apair of electrodes (for example, positioned at a distal end of a medicalinstrument, catheter or probe) and a processing device configured toexecute specific program instructions stored on a non-transitorycomputer-readable storage medium to process a resulting waveform thatformulates across the pair of electrodes to obtain impedancemeasurements at the first frequency and the second frequency. If theimpedance magnitude at the first and/or second frequency is above apredetermined threshold indicative of contact, the processing device isconfigured to, upon execution of stored instructions on thecomputer-readable storage medium, generate a first output indicative ofcontact. If the impedance magnitude at the first and/or second frequencyis below a predetermined threshold indicative of no contact, theprocessing device is configured to, upon execution of storedinstructions on the computer-readable storage medium, generate a secondoutput indicative of no contact. Processing the waveforms may compriseobtaining voltage and/or current measurements and calculating impedancemeasurements based on the voltage and/or current measurements ordirectly obtaining impedance measurements.

A method of determining whether a medical instrument is in contact witha target region (for example, tissue) based, at least in part, onimpedance measurements comprises delivering at least one signal having afirst frequency and a second frequency (for example, a multi-tonalwaveform) to a pair of electrodes or electrode portions and processing aresulting waveform that formulates across the pair of electrodes toobtain impedance measurements at the first frequency and the secondfrequency. If the impedance magnitude at the first frequency and/orsecond frequency is above a predetermined threshold indicative ofcontact, the method comprises generating a first output indicative ofcontact. If the impedance magnitude at the first frequency and/or secondfrequency is below a predetermined threshold indicative of no contact,the method comprises generating a second output indicative of nocontact.

A method of determining whether a medical instrument is in contact witha target region (for example, tissue) based, at least in part, onimpedance measurements may comprise applying a signal comprising amulti-tone waveform having a first frequency and a second frequency to apair of electrodes, processing the resulting waveform to obtainimpedance measurements at the first frequency and the second frequency,comparing values of the impedance measurements at the first frequencyand the second frequency to a known impedance of blood or a blood andsaline mixture (or other known tissue impedance), comparing values ofthe impedance measurements at the first and second frequency to eachother; and generating an output indicative of whether or not the medicalinstrument is in contact with tissue based on said comparisons. A systemfor determining whether a medical instrument is in contact with tissuebased, at least in part, on impedance measurements may comprise a signalsource configured to generate a multi-tone waveform or signal having afirst frequency and a second frequency to a pair of electrodes (forexample, at a distal end of a split-tip electrode catheter); and aprocessing device. The processing device may be configured to, uponexecution of stored instructions on a computer-readable storage medium,process the resulting waveform to obtain impedance measurements at thefirst frequency and the second frequency, compare values of theimpedance measurements at the first frequency and the second frequencyto a known impedance of blood or a blood and saline mixture, comparevalues of the impedance measurements at the first and second frequencyto each other and/or generate an output indicative of whether or not themedical instrument is in contact with tissue based on said comparisons.

In accordance with several embodiments, a method of determining whethera medical instrument comprising a pair of electrodes or electrodeportions is in contact with a target region (for example, tissue) based,at least in part, on impedance measurements comprises applying at leastone signal having a plurality of frequencies (for example, a multi-tonalwaveform) to a pair of electrodes of a medical instrument, andprocessing a resulting waveform that formulates across the pair ofelectrodes to obtain impedance measurements at a first frequency and asecond frequency of the plurality of frequencies. If a variation of theimpedance measurements across the range of frequencies has a model whoseparameter values are indicative of contact, the method comprisesgenerating a first output indicative of contact. If the variation of theimpedance measurements across the range of frequencies has a model whoseparameter values are indicative of no contact, the method comprisesgenerating a second output indicative of no contact. The model maycomprise a fitting function or a circuit model such as shown in FIG. 5B.A system for determining whether a medical instrument is in contact withtissue based, at least in part, on impedance measurements comprises asignal source configured to generate at least one signal having a firstfrequency and a second frequency to a pair of electrodes and aprocessing device. The processing device may be configured to, uponexecution of stored instructions on a computer-readable storage medium,apply at least one signal having a plurality of frequencies to a pair ofelectrodes of a medical instrument and process a resulting waveform thatformulates across the pair of electrodes to obtain impedancemeasurements at a first frequency and a second frequency of theplurality of frequencies. If a variation of the impedance measurementsacross the range of frequencies follows a model whose parameter valuesare indicative of contact the processor is configured to generate afirst output indicative of contact. If the variation of the impedancemeasurements across the range of frequencies follows a model whoseparameter values are indicative of no contact, the processor isconfigured to generate a second output indicative of no contact.Processing the waveforms to obtain impedance measurements may compriseobtaining voltage and/or current measurements and calculating impedancemeasurements based on the voltage and/or current measurements ordirectly obtaining impedance measurements.

In accordance with several embodiments, a method of determining whethertissue has been ablated by an ablation catheter comprising a pair ofelectrodes is provided. The method comprises applying one or moresignals having a first frequency and a second frequency (for example, amulti-tonal waveform) to a pair of electrodes along the ablationcatheter and processing a resulting waveform that formulates across thepair of electrodes to obtain impedance measurements at the firstfrequency and the second frequency. The method may comprise assessingabsolute change in the impedance as well as the slope or ratio betweenimpedance. If the first impedance measurement at the first and/or secondfrequency is greater than a known impedance level of blood and if aratio of the second impedance measurement to the first impedancemeasurement is above a predetermined threshold, the method comprisesgenerating a first output indicative of ablated tissue. If the firstimpedance measurement at the first and/or second frequency is greaterthan a known impedance level of blood and if a ratio of the secondimpedance measurement to the first impedance measurement is below apredetermined threshold, the method comprises generating a second outputindicative of viable tissue. Processing the waveforms to obtainimpedance measurements may comprise obtaining voltage and/or currentmeasurements and calculating impedance measurements based on the voltageand/or current measurements or directly obtaining impedancemeasurements.

In some embodiments, a phase of the impedance measurements at the firstfrequency and/or second frequency is compared to a known phase responsefor blood or a blood and saline mixture and utilized in conjunction withthe magnitude values of the impedance measurements to generate an outputindicative of whether or not the medical instrument is in contact withtissue. A system for determining whether tissue has been ablated by anablation catheter comprising a pair of electrodes or electrode portionsmay comprise a signal source configured to generate at least one signalhaving a first frequency and a second frequency to a pair of electrodesalong the ablation catheter and a processing device. The processingdevice may be configured to, upon execution of stored instructions on acomputer-readable storage medium, process a resulting waveform thatformulates across the pair of electrodes to obtain impedancemeasurements at the first frequency and the second frequency. If thefirst impedance measurement at the first and/or second frequency isgreater than a known impedance level of blood and if a ratio of thesecond impedance measurement to the first impedance measurement is abovea predetermined threshold, the processing device is configured togenerate a first output indicative of ablated tissue. If a ratio of thesecond impedance measurement to the first impedance measurement is belowa predetermined threshold, the processor is configured to generate asecond output indicative of viable (for example, unablated) tissue.Processing the waveforms to obtain impedance measurements may compriseobtaining voltage and/or current measurements and calculating impedancemeasurements based on the voltage and/or current measurements ordirectly obtaining impedance measurements.

Processing the resulting waveform may comprise applying a transform (forexample, a Fourier transform) to the waveform to obtain the impedancemeasurements. In some embodiments, the first frequency and the secondfrequency are within a range between 5 kHz and 1000 kHz. In oneembodiment, the second frequency is higher than the first frequency. Theimpedance measurements may be obtained simultaneously or sequentially.The second frequency may be at least 20 kHz higher than the firstfrequency. In one embodiment, the first frequency is between 10 kHz and100 kHz (for example, between 10 KHz and 30 kHz, between 15 kHz and 40kHz, between 20 kHz and 50 kHz, between 30 kHz and 60 kHz, between 40kHz and 80 kHz, between 50 kHz and 90 kHz, between 60 kHz and 100 kHz,overlapping ranges thereof, 20 kHz or any values from 10 kHz and 100kHz) and the second frequency is between 400 kHz and 1000 kHz (forexample, between 400 kHz and 600 kHz, between 450 kHz and 750 kHz,between 500 kHz and 800 kHz, between 600 kHz and 850 kHz, between 700kHz and 900 kHz, between 800 kHz and 1000 kHz, overlapping rangesthereof, 800 kHz, or any values from 400 kHz to 1000 kHz). Thepredetermined threshold may have a value between 0.5 and 0.9. In someembodiments, generating a first output and generating a second outputfurther comprises causing the first output or the second output to bedisplayed on a display (for example via one or more display drivers).The output may comprise textual information, quantitative measurementsand/or qualitative assessments indicative of contact state. In someembodiments, the output includes an amount of contact forcecorresponding to the level of contact (for example, grams of force).

A method of determining whether a medical instrument having a pair ofelectrodes or electrode portions is in contact with a target region (forexample, tissue) based, at least in part, on impedance measurements maycomprise obtaining a first impedance measurement at a first frequencywithin a range of frequencies, obtaining a second impedance measurementat a second frequency within the range of frequencies and obtaining athird impedance measurement at a third frequency within the range offrequencies. If a variation of the impedance measurements across therange of frequencies is above a predetermined threshold indicative ofcontact, the method comprises generating a first output indicative ofcontact. If the variation of the impedance measurements across the rangeof frequencies is below the predetermined threshold, the methodcomprises generating a second output indicative of no contact. Theimpedance measurements may be calculated based on voltage and/or currentmeasurements or may be directly-measured impedance measurements.

The range of frequencies may be between 5 kHz and 5 MHz (for example,between 5 kHz and 1000 kHz, between 1 MHz and 3 MHz, between 2.5 MHz and5 MHz, or overlapping ranges thereof). In one embodiment, the firstfrequency is between 10 kHz and 100 kHz (for example, between 10 KHz and30 kHz, between 15 kHz and 40 kHz, between 20 kHz and 50 kHz, between 30kHz and 60 kHz, between 40 kHz and 80 kHz, between 50 kHz and 90 kHz,between 60 kHz and 100 kHz, overlapping ranges thereof, 20 kHz or anyvalues from 10 kHz and 100 kHz) and the second frequency is between 400kHz and 1000 kHz (for example, between 400 kHz and 600 kHz, between 450kHz and 750 kHz, between 500 kHz and 800 kHz, between 600 kHz and 850kHz, between 700 kHz and 900 kHz, between 800 kHz and 1000 kHz,overlapping ranges thereof, 800 kHz, or any values from 400 kHz to 1000kHz) and the third frequency is between 20 kHz and 800 kHz. Thepredetermined threshold may be a value between 0.5 and 0.9. In someembodiments, generating a first output and generating a second outputcomprises causing the first output or the second output to be displayedon a display. The output may comprise textual information indicative ofcontact. In one embodiment, the output comprises a quantitativemeasurement and/or qualitative assessment of contact.

In some embodiments, the distal end portion of the medical instrumentcomprises a high-resolution electrode assembly comprising a firstelectrode portion and second electrode portion spaced apart andinsulated from the first electrode portion (for example, a split-tipelectrode assembly or combination radiofrequency electrode). The controlunit may comprise a contact detection subsystem or module configured toreceive signals from the high-resolution electrode assembly and thecontrol unit (for example, processor) of the contact detection subsystemor module or a separate processor may be configured (for example,specifically programmed with instructions stored in or on anon-transitory computer-readable medium) to determine a level of contactor a contact state with tissue (for example, cardiac tissue) based onthe received signals from the high-resolution electrode assembly and tomodulate the opposition force provided by the opposition force motorbased, at least in part, on the determined level of contact, or thecontact state. The control unit may further comprise a power deliverymodule configured to apply radiofrequency power to the high-resolutionelectrode assembly at a level sufficient to effect ablation of tissue incontact with at least a portion of the distal end portion of the medicalinstrument.

In some embodiments, the control unit (for example, processor) isconfigured to generate output indicative of the level of contact fordisplay on a display coupled to the control unit (for example, via oneor more display drivers). In various embodiments, the output is based ona contact function determined based on one or more criteria combiningmultiple electrical parameter measurements (such as voltagemeasurements, current measurements or impedance measurements). In oneembodiment, the contact function is determined by summing a weightedcombination of impedance (for example, bipolar impedance) measurementsthat are directly measured or that are calculated based on voltageand/or current measurements. In one embodiment, the contact function isbased on one or more if-then case conditional criteria. In oneembodiment, the impedance measurements comprise one or more of animpedance magnitude determined by the contact detection subsystem at afirst frequency, a ratio of impedance magnitudes at the first frequencyand a second frequency and a phase of a complex impedance measurement atthe second frequency. The second frequency may be higher than the firstfrequency (for example, at least 20 kHz higher than the firstfrequency). In some embodiments, the first frequency and the secondfrequency are between 5 kHz and 1000 kHz. In one embodiment, the firstfrequency is between 10 kHz and 100 kHz (for example, between 10 KHz and30 kHz, between 15 kHz and 40 kHz, between 20 kHz and 50 kHz, between 30kHz and 60 kHz, between 40 kHz and 80 kHz, between 50 kHz and 90 kHz,between 60 kHz and 100 kHz, overlapping ranges thereof, 20 kHz or anyvalues from 10 kHz and 100 kHz) and the second frequency is between 400kHz and 1000 kHz (for example, between 400 kHz and 600 kHz, between 450kHz and 750 kHz, between 500 kHz and 800 kHz, between 600 kHz and 850kHz, between 700 kHz and 900 kHz, between 800 kHz and 1000 kHz,overlapping ranges thereof, 800 kHz, or any values from 400 kHz to 1000kHz); however, other frequencies may be used as desired and/or required.In some embodiments, the frequencies at which impedance measurements areobtained are outside treatment (for example, ablation) frequency ranges.In some embodiments, filters (such as bandpass filters) are used toisolate the treatment frequency ranges from the impedance measurementfrequency ranges.

In some embodiments, the handle of the medical instrument furthercomprises a motion detection element (for example, at least one of anaccelerometer and a gyroscope). In some embodiments, the first motor isconfigured to be actuated only when the motion detection element isdetecting motion of the handle.

In accordance with several embodiments, a method of determining acontact state of a distal end portion of a medical instrument with atarget region, for example, tissue, comprises applying at least onesignal having a plurality of frequencies to a pair of electrodes orelectrode portions of a combination electrode assembly positioned alonga distal end portion of a medical instrument. The method comprisesprocessing a resulting waveform that formulates across the pair ofelectrodes to obtain a first impedance measurement at a first frequencyof the plurality of frequencies and processing the resulting waveformthat formulates across the pair of electrodes to obtain a secondimpedance measurement at a second frequency of the plurality offrequencies. The method further comprises determining a magnitude of thefirst impedance measurement, determining a magnitude and a phase of thesecond impedance measurement and applying a contact function (forexample, via execution of a computer program stored on a non-transitorycomputer storage medium) to calculate a contact indication valueindicative of a state of contact between the distal end portion of themedical instrument and the target region (for example, cardiac tissue).The contact function may be determined by summing a weighted combinationof the magnitude of the first impedance measurement, a ratio of themagnitudes of the first impedance measurement and the second impedancemeasurement, and the phase of the second impedance measurement. Invarious embodiments, the first frequency and the second frequency aredifferent. In one embodiment, the second frequency is higher than thefirst frequency.

The method may further comprise generating output corresponding to thecontact indication value for display on a display monitor (for example,via one or more display drivers). In some embodiments, the outputcomprises a qualitative and/or a quantitative output. The output maycomprise a numerical value between 0 and 1 or between 0 and 1.5, withvalues above 1 indicating excessive contact. In some embodiments, theoutput comprises a percentage value or a number corresponding to anamount of contact force (for example, grams of contact force). Theoutput may comprise a color and/or pattern indicative of the contactstate and/or one or more of a gauge, a bar, or a scale.

In accordance with several embodiments, a system for determining acontact state of a distal end portion of a medical instrument with atarget region (for example, tissue, based, at least in part, onelectrical parameter measurements consists essentially of or comprises asignal source configured to generate at least one signal having a firstfrequency and a second frequency to be applied to a pair of electrodemembers of a combination electrode assembly (for example, two electrodemembers separated by a gap). The system also consists essentially of orcomprises a processing device configured to (a) cause the signal sourceto generate and apply the at least one signal to the pair of electrodemembers, (b) process a resulting waveform that formulates across thepair of electrode members to obtain a first electrical measurement atthe first frequency, (c) process the resulting waveform that formulatesacross the pair of electrode members to obtain a second electricalmeasurement at the second frequency of the plurality of frequencies, (d)determine an impedance magnitude based on the first electricalmeasurement, (e) determine an impedance magnitude and a phase based onthe second electrical measurement, and (f) calculate a contactindication value indicative of a state of contact between the distal endportion of the medical instrument and the target region based on acriterion combining the impedance magnitude based on the firstelectrical measurement, a ratio of the impedance magnitudes based on thefirst and second electrical measurements, and the phase based on thesecond electrical measurement. The electrical measurements may comprisevoltage, current, and/or other electrical parameter measurements fromwhich impedance measurements (such as impedance magnitude or phase) maybe calculated or may comprise directly-obtained impedance measurements.The criterion may comprise a weighted combination of the impedancemagnitude based on the first electrical measurement, a ratio of theimpedance magnitudes based on the first and second electricalmeasurements, and the phase based on the second electrical measurementor the criterion may comprise an if-then case conditional criterion.

In some embodiments, the system further comprises the medicalinstrument, which may be a radiofrequency ablation catheter. The firstfrequency and the second frequency may be different. In someembodiments, the second frequency is higher than the first frequency. Inother embodiments, the second frequency is lower than the firstfrequency. In some embodiments, the first frequency and the secondfrequency are between 5 kHz and 1000 kHz (for example, between 5 kHz and50 kHz, between 10 kHz and 100 kHz, between 50 kHz and 200 kHz, between100 kHz and 500 kHz, between 200 kHz and 800 kHz, between 400 kHz and1000 kHz, or overlapping ranges thereof). In various embodiments, thetwo frequencies are at least 20 kHz apart in frequency.

In some embodiments, the processor is further configured to generateoutput corresponding to the contact indication value for display on adisplay monitor, upon execution of specific instructions stored in or ona computer-readable medium. In some embodiments, the output comprises anumerical value between 0 and 1. In some embodiments, the outputcomprises a qualitative output (such as a color and/or patternindicative of the contact state). In some embodiments, the outputcomprises one or more of a gauge, a bar, a meter or a scale. In oneembodiment, the output comprises a virtual gauge having a plurality ofregions (for example, two, three, four, five or more than five regionsor segments) indicative of varying levels of contact, or contact states.The plurality of regions may be represented in different colors. Each ofthe plurality of regions may correspond to a different range ofnumerical values indicative of varying levels of contact.

In accordance with several embodiments, a system for displaying acontact state of a distal tip of a medical instrument with a targetregion (for example, body tissue) on a patient monitor comprises aprocessor configured to generate output for display on the patientmonitor. The output may be generated on a graphical user interface onthe patient monitor. In one embodiment, the output comprises a graphthat displays a contact function indicative of a contact state between adistal tip of a medical instrument and body tissue calculated by aprocessing device based, at least in part, on impedance measurementsobtained by the medical instrument. The graph may be a scrollingwaveform. The output also comprises a gauge separate from the graph thatindicates a real-time state of contact corresponding to a real-timenumerical value of the contact function displayed by the graph. Thegauge includes a plurality of regions indicative of varying contactstates. In some embodiments, each one of the plurality of regions isoptionally displayed in a different color or graduation to provide aqualitative indication of the real-time state of contact. In oneembodiment, the gauge consists of three regions or segments. The threeregions may be colored red, yellow and green. In another embodiment, thegauge consists of four regions or segments. The four regions may becolored red, orange, yellow and green. Each of the plurality of regionsmay correspond to a different range of numerical values indicative ofthe current contact state. The gauge may comprise a pointer thatindicates a level on the gauge corresponding to the real-time numericalvalue of the contact function. The real-time numerical value may rangebetween 0 and 1 or between 0 and 1.25 or between 0 and 1.5. Values above1 may generate a “contact alert” to the clinician to prevent excessivecontact, which could result in perforation of tissue.

The output may also comprise other graphs or waveforms of individualcomponents of impedance measurements (for example, impedance magnitudeand phase) at multiple frequencies or of comparisons (for example, aslope) between two impedance measurements (for example, impedancemagnitude at two different frequencies).

In some embodiments, the contact function is calculated based on aweighted combination of a magnitude of a first impedance measurement ata first frequency, a ratio of the magnitudes of the first impedancemeasurement and a second impedance measurement at a second frequencydifferent from the first frequency, and the phase of the secondimpedance measurement at the second frequency. In one embodiment, thesecond frequency is higher than the first frequency. In anotherembodiment, the second frequency is lower than the first frequency. Thefirst frequency and the second frequency may be between 5 kHz and 1000kHz. In some embodiments, the system further comprises the patientmonitor.

In accordance with several embodiments, a system for assessing a levelof contact between a distal end portion of an ablation catheter having apair of spaced-apart electrode members of a combination electrodeassembly and target region, e.g., tissue, comprises a signal sourceconfigured to generate signals having at least a first frequency and asecond frequency to be applied to the pair of spaced-apart electrodemembers. The system also comprises a processor configured to, uponexecution of specific program instructions stored on a computer-readablestorage medium, measure network parameters at an input of a networkmeasurement circuit comprising a plurality of hardware componentsbetween the signal source and the pair of spaced-apart electrodemembers. The processor may also be configured (for example, specificallyprogrammed, constructed or designed) to determine an aggregate effect ona measured network parameter value caused by the hardware components ofthe network measurement circuit, remove the aggregate effect to resultin a corrected network parameter value between the pair of spaced-apartelectrode members, and determine a level of contact based, at least inpart, on the corrected network parameter value.

In some embodiments, the processor is configured to generate an outputindicative of the level of contact for display. The signal source may belocated within a radiofrequency generator or within the ablationcatheter. The processor may be configured to measure network parametersat at least two frequencies (for example, two frequencies, threefrequencies, four frequencies or more than four frequencies). In someembodiments, the frequencies are between 5 kHz and 1000 kHz. Inembodiments involving two frequencies, the second frequency may be atleast 20 kHz higher than the first frequency. For example, the firstfrequency may be between 10 kHz and 100 kHz and the second frequency isbetween 400 kHz and 1000 kHz. A third frequency may be higher than thefirst frequency and lower than the second frequency (for example, thethird frequency may be between 20 kHz and 120 kHz).

The network parameters may comprise scattering parameters or otherelectrical parameters (such as voltage, current, impedance). The networkparameter values may comprise, for example, voltage and current valuesor impedance values either directly measured or determined from voltageand/or current values. Impedance values may comprise impedance magnitudevalues and impedance phase values. The impedance magnitude values may beobtained at two or more frequencies and slopes may be determined betweenmagnitude values at different frequencies. The impedance phase valuesmay be obtained at one or more frequencies.

In accordance with several embodiments, a method of assessing a level ofcontact determination of a distal end portion of an ablation catheterhaving a pair of spaced-apart electrode members comprises measuringnetwork parameters at an input of a network parameter circuit ofhardware components between a signal source and the pair of spaced-apartelectrode members. The method also comprises determining an aggregateeffect on a measured network parameter value determined from the networkparameters caused by the hardware components, removing the aggregateeffect to result in a corrected network parameter value between the pairof spaced-apart electrode members, and determining a level of contactbased, at least in part, on the corrected network parameter value.

Measuring network parameters may comprise measuring network parametersat a plurality of frequencies. In some embodiments, determining anaggregate effect on the measured network parameter value caused by thehardware components of the network parameter circuit comprises measuringnetwork parameters associated with each individual hardware component.In some embodiments, determining an aggregate effect on the measurednetwork parameter value caused by the hardware components of the networkparameter circuit comprises combining the network parameters of theindividual hardware components into total network parameters at aplurality of frequencies. Removing the aggregate effect so as to isolatean actual network parameter value between the pair of spaced-apartelectrode members may comprise de-embedding the total network parametersfrom a measured input reflection coefficient to result in an actualreflection coefficient corresponding to the actual network parametervalue. In some embodiments, the method is performed automatically by aprocessor.

The processing device (for example, processor or controller) may beconfigured to perform operations recited herein upon execution ofinstructions stored within memory or a non-transitory storage medium.The methods summarized above and set forth in further detail below maydescribe certain actions taken by a practitioner; however, it should beunderstood that they can also include the instruction of those actionsby another party. For example, actions such as “terminating energydelivery” include “instructing the terminating of energy delivery.”Further aspects of embodiments of the invention will be discussed in thefollowing portions of the specification. With respect to the drawings,elements from one figure may be combined with elements from the otherfigures.

According to some embodiments, an ablation system consists essentiallyof a catheter, an ablation member (e.g., a RF electrode, a split-tipelectrode, another type of high-resolution electrode, etc.), anirrigation conduit extending through an interior of the catheter to ornear the ablation member, at least one electrical conductor (e.g., wire,cable, etc.) to selectively activate the ablation member and at leastone heat transfer member that places at least a portion of the ablationmember (e.g., a proximal portion of the ablation member) in thermalcommunication with the irrigation conduit, at least one heat shuntmember configured to effectively transfer heat away from the electrodeand/or tissue being treated and a plurality of temperature sensors(e.g., thermocouples) located along two different longitudinal locationsof the catheter, wherein the temperature sensors are thermally isolatedfrom the electrode and configured to detect temperature of tissue at adepth.

The methods summarized above and set forth in further detail below maydescribe certain actions taken by a practitioner; however, it should beunderstood that they can also include the instruction of those actionsby another party. For example, actions such as “terminating energydelivery” include “instructing the terminating of energy delivery.”Further aspects of embodiments of the invention will be discussed in thefollowing portions of the specification. With respect to the drawings,elements from one figure may be combined with elements from the otherfigures.

BRIEF DESCRIPTION OF THE DRAWINGS

These and other features, aspects and advantages of the presentapplication are described with reference to drawings of certainembodiments, which are intended to illustrate, but not to limit, theconcepts disclosed herein. The attached drawings are provided for thepurpose of illustrating concepts of at least some of the embodimentsdisclosed herein and may not be to scale.

FIG. 1 schematically illustrates one embodiment of an energy deliverysystem configured to selectively ablate or otherwise heat targetedtissue of a subject;

FIG. 2 illustrates a side view of a system's catheter comprises ahigh-resolution-tip design according to one embodiment;

FIG. 3 illustrates a side view of a system's catheter comprises ahigh-resolution-tip design according to another embodiment;

FIG. 4 illustrates a side view of a system's catheter comprises ahigh-resolution-tip design according to yet another embodiment;

FIG. 5 illustrates an embodiment of a system's catheter comprising twohigh-resolution-section electrodes each consisting of separate sectionscircumferentially distributed on the catheter shaft;

FIG. 6 schematically illustrates one embodiment of a high-pass filteringelement consisting of a coupling capacitor. The filtering element can beincorporated into a system's catheter that comprises ahigh-resolution-tip design;

FIG. 7 schematically illustrates one embodiment of four high-passfiltering elements comprising coupling capacitors. The filteringelements can operatively couple, in the operating RF frequency range,the separate electrode sections of a system's catheter electrodes, e.g.,those illustrated in FIG. 5;

FIG. 8 illustrates embodiments of EKGs obtained from ahigh-resolution-tip electrode systems disclosed herein configured todetect whether an ablation procedure has been adequately performed;

FIG. 9 illustrates a perspective view of an ablation system's cathetercomprising an electrode and heat shunt network to facilitate thetransfer of heat to an irrigation conduit during use, according to oneembodiment;

FIG. 10 illustrates a partially exposed view of the system of FIG. 9;

FIG. 11 illustrates a perspective view of an ablation system's cathetercomprising an electrode and heat shunt network to facilitate thetransfer of heat to an irrigation conduit during use, according toanother embodiment;

FIG. 12 illustrates a cross-sectional view of an ablation system'scatheter comprising an electrode and heat shunt network to facilitatethe transfer of heat to an irrigation conduit during use, according toone embodiment;

FIG. 13 illustrates a partial cross-sectional perspective view of oneembodiment of an ablation system's catheter comprising an openirrigation cooling system;

FIG. 14 illustrates a partial cross-sectional perspective view of oneembodiment of an ablation system's catheter comprising a closedirrigation cooling system;

FIG. 15 illustrates a partial cross-sectional perspective view ofanother embodiment of an ablation system's catheter;

FIG. 16A illustrates a side perspective view of a distal end of oneembodiment of a split-tip RF ablation system comprising heat transfer(e.g. heat shunt) members;

FIG. 16B illustrates a partial cross-sectional perspective view of thesystem of FIG. 16A;

FIG. 16C illustrates a partial cross-sectional perspective view ofanother embodiment of an ablation system comprising a split-tipelectrode and heat transfer (e.g. heat shunt) members;

FIG. 17A illustrates a side perspective view of a distal end of oneembodiment of a split-tip RF ablation system comprising heat transfer(e.g. heat shunt) members and fluid outlets extending through a proximalelectrode or slug;

FIG. 17B illustrates a partial cross-sectional perspective view of thesystem of FIG. 17A;

FIG. 18A illustrates a perspective view of a distal portion of anopen-irrigated ablation catheter having multiple temperature-measurementdevices, according to one embodiment;

FIGS. 18B and 18C illustrate a perspective view and a cross-sectionalview, respectively, of a distal portion of an open-irrigated ablationcatheter having multiple temperature-measurement devices, according toanother embodiment;

FIG. 18D illustrates a perspective view of a distal portion of anablation catheter having multiple temperature-measurement devices,according to another embodiment;

FIGS. 18E and 18F illustrate a perspective view and a cross-sectionalview, respectively, of a distal portion of an ablation catheter showingisolation of the distal temperature-measurement devices from anelectrode tip, according to one embodiment;

FIG. 19A illustrates a perspective view of a distal portion of aclosed-irrigation ablation catheter having multipletemperature-measurement devices, according to one embodiment;

FIGS. 19B and 19C illustrate a perspective view and a cross-sectionalview, respectively, of a distal portion of a closed-irrigation ablationcatheter having multiple temperature-measurement devices, according toanother embodiment;

FIG. 20 illustrates a perspective view of a distal portion of anopen-irrigated ablation catheter comprising a non-split-tip designaccording to one embodiment;

FIG. 21A schematically illustrates a distal portion of an open-irrigatedablation catheter in contact with tissue to be ablated in aperpendicular orientation and a lesion formed using the ablationcatheter, according to one embodiment;

FIG. 21B schematically illustrates a distal portion of an open-irrigatedablation catheter in contact with tissue to be ablated in a parallelorientation and a lesion formed using the ablation catheter, accordingto one embodiment;

FIG. 22A is a graph illustrating that temperature of a lesion peak maybe correlated to the temperature of the temperature-measurement devicesby a correction factor or function, according to one embodiment;

FIG. 22B is a plot showing an estimated peak temperature determined byan embodiment of an ablation catheter having multipletemperature-measurement devices compared against actual tissuemeasurements at various depths within a tissue;

FIGS. 23A and 23B illustrate plots showing temperature measurementsobtained by the multiple temperature-measurement devices of anembodiment of an ablation catheter for a parallel orientation and anoblique orientation, respectively;

FIG. 24 schematically illustrates one embodiment of variable frequencybeing applied to the split-tip electrode design of FIG. 2 to determinewhether the split-tip electrode is in contact with tissue;

FIG. 25A is a plot showing normalized resistance of blood/saline andtissue across a range of frequencies;

FIG. 25B is a plot of a four tone waveform utilized for impedancemeasurements;

FIG. 25C is a plot of impedance vs. frequency, with tones at fourfrequencies;

FIG. 25D schematically illustrates one embodiment of a contact sensingsubsystem configured to perform contact sensing functions whilesimultaneously conducting electrogram (EGM) measurements, in accordancewith one embodiment;

FIG. 26A illustrates zero crossings of a frequency spectrum and is usedto illustrate that switching between frequencies may be designed tooccur at the zero crossings to avoid interference at EGM frequencies;

FIG. 26B schematically illustrates one embodiment of a circuit model todescribe the behavior of the impedance of tissue or blood orblood/saline combination, as measured across two electrodes or electrodeportions;

FIG. 26C schematically illustrates one embodiment of a circuitconfigured to switch between contact sensing circuitry in standby modeand radiofrequency energy delivery circuitry in treatment mode, inaccordance with one embodiment;

FIG. 27 schematically illustrates one embodiment of a circuit configuredto perform contact sensing functions while radiofrequency energy isbeing delivered, in accordance with one embodiment;

FIG. 28 is a plot of impedance of an LC circuit element across a rangeof frequencies;

FIG. 29 is a plot showing resistance, or impedance magnitude, values ofablated tissue, viable tissue and blood across a range of frequencies;

FIG. 30 is a plot showing the phase of impedance values of ablatedtissue, viable tissue and blood across a range of frequencies;

FIG. 31 illustrates one embodiment of a sensing algorithm that utilizesimpedance magnitude, ratio of impedance magnitude at two frequencies,and impedance phase data to determine contact state as well as tissuestate;

FIG. 32 illustrates an embodiment of a contact criterion process, andFIG. 32A illustrates an embodiment of a sub-process of the contactcriterion process of FIG. 32;

FIG. 33 illustrates an embodiment of a graphical user interface of adisplay of output indicative of tissue contact by a high resolutioncombination electrode device;

FIG. 34A illustrates a schematic representation of possible hardwarecomponents of a network measurement circuit;

FIG. 34B illustrates a schematic representation of an embodiment of anauto-calibration circuit configured to calibrate (for example,automatically) the network measurement circuit so as to remove theeffects of one or more hardware components present in the circuit; and

FIG. 34C illustrates a schematic representation of one embodiment of anequivalent circuit model for a hardware component present in animpedance measurement circuit.

DETAILED DESCRIPTION

According to some embodiments, successful electrophysiology proceduresrequire precise knowledge about the anatomic substrate being targeted.Additionally, it may be desirable to evaluate the outcome of an ablationprocedure within a short period of time after the execution of theprocedure (e.g., to confirm that the desired clinical outcome wasachieved). Typically, ablation catheters include only regular mappingelectrodes (e.g., ECG electrodes). However, in some embodiments, it maybe desirable for such catheters to incorporate high-resolution mappingcapabilities. In some embodiments, high-resolution mapping electrodescan provide more accurate and more detailed information about theanatomic substrate and about the outcome of ablation procedures. Forexample, such high-resolution mapping electrodes can allow theelectrophysiology (EP) practitioner to evaluate the morphology ofelectrograms, their amplitude and width and/or to determine changes inpacing thresholds. According to some arrangements, morphology, amplitudeand/or pacing threshold are accepted as reliable EP markers that provideuseful information about the outcome of ablation. Thus, high-resolutionelectrodes are defined as any electrode(s) capable of deliveringablative or other energy to tissue capable of transferring heat to/fromsuch tissue, while being capable of obtaining accurate mapping data ofadjacent tissue, and include, without limitation, split-tip RFelectrodes, other closely oriented electrodes or electrode portionsand/or the like.

According to some embodiments, the present application disclosesdevices, systems and/or methods that include one or more of thefollowing features: a high-resolution electrode (e.g., split tipelectrode), heat shunting concepts to help dissipate heat away from theelectrode and/or the tissue of the subject being treated, multipletemperature sensors located along the exterior of the device todetermine, among other things, temperature of the subject at a depth andcontact sensing features that help determine if and to what extent thedevice is contacting targeted tissue.

Several embodiments of the invention are particularly advantageousbecause they include one, several or all of the following benefits: (i)provides the ability to obtain accurate tissue mapping data using thesame electrode that delivers the ablative energy, (ii) reduces proximaledge heating, (iii) reduces likelihood of char or thrombus formation,(iv) provides feedback that may be used to adjust ablation procedures inreal time, (v) provides noninvasive temperature measurements, (vi) doesnot require use of radiometry; (vii) provides tissue temperaturemonitoring and feedback during irrigated or non-irrigated ablation; and(vii) provides multiple forms of output or feedback to a user; and (ix)provides safer and more reliable ablation procedures.

High-Resolution Electrode

According to some embodiments, various implementations of electrodes(e.g., radiofrequency or RF electrodes) that can be used forhigh-resolution mapping are disclosed herein. For example, as discussedin greater detail herein, an ablation or other energy delivery systemcan comprise a high-resolution-tip design, wherein the energy deliverymember (e.g., radiofrequency electrode) comprises two or more separateelectrodes or electrode portions. As also discussed herein, in someembodiments, such separate electrodes or electrode portions can beadvantageously electrically coupled to each other (e.g., to collectivelycreate the desired heating or ablation of targeted tissue).

FIG. 1 schematically illustrates one embodiment of an energy deliverysystem 10 that is configured to selectively ablate, stimulate, modulateand/or otherwise heat or treat targeted tissue (e.g., cardiac tissue,pulmonary vein, other vessels or organs, etc.). Although certainembodiments disclosed herein are described with reference to ablationsystems and methods, any of the systems and methods can be used tostimulate, modulate, heat and/or otherwise affect tissue, with orwithout partial or complete ablation, as desired or required. As shown,the system 10 can include a medical instrument 20 (e.g., catheter)comprising one or more energy delivery members 30 (e.g., radiofrequencyelectrodes) along a distal end of the medical instrument 20. The medicalinstrument can be sized, shaped and/or otherwise configured to be passedintraluminally (e.g., intravascularly) through a subject being treated.In various embodiments, the medical instrument 20 comprises a catheter,a shaft, a wire, and/or other elongate instrument. In other embodiments,the medical instrument is not positioned intravascularly but ispositioned extravascularly via laparoscopic or open surgical procedures.In various embodiments, the medical instrument 20 comprises a catheter,a shaft, a wire, and/or other elongate instrument. In some embodiments,one or more temperature sensing devices or systems 60 (e.g.,thermocouples, thermistors, etc.) may be included at the distal end ofthe medical instrument 20, or along its elongate shaft or in its handle.The term “distal end” does not necessarily mean the distal terminus ordistal end. Distal end could mean the distal terminus or a locationspaced from the distal terminus but generally at a distal end portion ofthe medical instrument 20.

In some embodiments, the medical instrument 20 is operatively coupled toone or more devices or components. For example, as depicted in FIG. 1,the medical instrument 20 can be coupled to a delivery module 40 (suchas an energy delivery module). According to some arrangements, theenergy delivery module 40 includes an energy generation device 42 thatis configured to selectively energize and/or otherwise activate theenergy delivery member(s) 30 (for example, radiofrequency electrodes)located along the medical instrument 20. In some embodiments, forinstance, the energy generation device 42 comprises a radiofrequencygenerator, an ultrasound energy source, a microwave energy source, alaser/light source, another type of energy source or generator, and thelike, and combinations thereof. In other embodiments, energy generationdevice 42 is substituted with or use in addition to a source of fluid,such a cryogenic fluid or other fluid that modulates temperature.Likewise, the delivery module (e.g., delivery module 40), as usedherein, can also be a cryogenic device or other device that isconfigured for thermal modulation.

With continued reference to the schematic of FIG. 1, the energy deliverymodule 40 can include one or more input/output devices or components 44,such as, for example, a touchscreen device, a screen or other display, acontroller (e.g., button, knob, switch, dial, etc.), keypad, mouse,joystick, trackpad, or other input device and/or the like. Such devicescan permit a physician or other user to enter information into and/orreceive information from the system 10. In some embodiments, the outputdevice 44 can include a touchscreen or other display that providestissue temperature information, contact information, other measurementinformation and/or other data or indicators that can be useful forregulating a particular treatment procedure.

According to some embodiments, the energy delivery module 40 includes aprocessor 46 (e.g., a processing or control unit) that is configured toregulate one or more aspects of the treatment system 10. The module 40can also comprise a memory unit or other storage device 48 (e.g.,computer readable medium) that can be used to store operationalparameters and/or other data related to the operation of the system 10.In some embodiments, the processor 46 is configured to automaticallyregulate the delivery of energy from the energy generation device 42 tothe energy delivery member 30 of the medical instrument 20 based on oneor more operational schemes. For example, energy provided to the energydelivery member 30 (and thus, the amount of heat transferred to or fromthe targeted tissue) can be regulated based on, among other things, thedetected temperature of the tissue being treated.

According to some embodiments, the energy delivery system 10 can includeone or more temperature detection devices, such as, for example,reference temperature devices (e.g., thermocouples, thermistors, etc.)and/or the like. For example, in some embodiments, the device furthercomprises a one or more temperature sensors or othertemperature-measuring devices to help determine a peak (e.g., high orpeak, low or trough, etc.) temperature of tissue being treated. In someembodiments, the temperature sensors (e.g., thermocouples) located at,along and/or near the ablation member (e.g., RF electrode) can help withthe determination of whether contact is being made between the ablationmember and targeted tissue (and/or to what degree such contact is beingmade). In some embodiments, such peak temperature is determined withoutthe use of radiometry. Additional details regarding the use oftemperature sensors (e.g., thermocouples) to determine peak tissuetemperature and/or to confirm or evaluate tissue contact are providedherein.

With reference to FIG. 1, the energy delivery system 10 comprises (or isin configured to be placed in fluid communication with) an irrigationfluid system 70. In some embodiments, as schematically illustrated inFIG. 1, such a fluid system 70 is at least partially separate from theenergy delivery module 40 and/or other components of the system 10.However, in other embodiments, the irrigation fluid system 70 isincorporated, at least partially, into the energy delivery module 40.The irrigation fluid system 70 can include one or more pumps or otherfluid transfer devices that are configured to selectively move fluidthrough one or more lumens or other passages of the catheter 20. Suchfluid can be used to selectively cool (e.g., transfer heat away from)the energy delivery member 30 during use.

FIG. 2 illustrates one embodiment of a distal end of a medicalinstrument (e.g., catheter) 20. As shown, the catheter 20 can include ahigh-resolution tip design, such that there are two adjacent electrodesor two adjacent electrode portions 30A, 30B separated by a gap G.According to some embodiments, as depicted in the configuration of FIG.2, the relative length of the different electrodes or electrode portions30A, 30B can vary. For example, the length of the proximal electrode 30Bcan be between 1 to 20 times (e.g., 1-2, 2-3, 3-4, 4-5, 5-6, 6-7, 7-8,8-9, 9-10, 10-11, 11-12, 12-13, 13-14, 14-15, 15-16, 16-17, 17-18,18-19, 19-20, values between the foregoing ranges, etc.) the length ofthe distal electrode 30A, as desired or required. In other embodiments,the length of the proximal electrode 30B can be greater than 20 times(e.g., 20-25, 25-30, more than 30 times, etc.) the length of the distalelectrode 30A. In yet other embodiments, the lengths of the distal andproximal electrodes 30A, 30B are about equal. In some embodiments, thedistal electrode 30A is longer than the proximal electrode 30B (e.g., by1 to 20 times, such as, for example, 1-2, 2-3, 3-4, 4-5, 5-6, 6-7, 7-8,8-9, 9-10, 10-11, 11-12, 12-13, 13-14, 14-15, 15-16, 16-17, 17-18,18-19, 19-20, values between the foregoing ranges, etc.).

In some embodiments, the distal electrode or electrode portion 30A is0.5 mm long. In other embodiments, the distal electrode or electrodeportion 30A is between 0.1 mm and 1 mm long (e.g., 0.1-0.2, 0.2-0.3,0.3-0.4, 0.4-0.5, 0.5-0.6, 0.6-0.7, 0.7-0.8, 0.8-0.9, 0.9-1 mm, valuesbetween the foregoing ranges, etc.). In other embodiments, the distalelectrode or electrode portion 30A is greater than 1 mm in length, asdesired or required. In some embodiments, the proximal electrode orelectrode portion 30B is 2 to 4 mm long (e.g., 2-2.5, 2.5-3, 3-3.5,3.5-4 mm, lengths between the foregoing, etc.). However, in otherembodiments, the proximal electrode portion 30B is greater than 4 mm(e.g., 4-5, 5-6, 6-7, 7-8, 8-9, 9-10 mm, greater than 10 mm, etc.) orsmaller than 1 mm (e.g., 0.1-0.5, 0.5-1, 1-1.5, 1.5-2 mm, lengthsbetween the foregoing ranges, etc.), as desired or required. Inembodiments where the high-resolution electrodes are located on cathetershafts, the length of the electrodes can be 1 to 5 mm (e.g., 1-2, 2-3,3-4, 4-5 mm, lengths between the foregoing, etc.). However, in otherembodiments, the electrodes can be longer than 5 mm (e.g., 5-6, 6-7,7-8, 8-9, 9-10, 10-15, 15-20 mm, lengths between the foregoing, lengthsgreater than 20 mm, etc.), as desired or required.

As noted above, the use of a high-resolution tip design can permit auser to simultaneously ablate or otherwise thermally treat targetedtissue and map (e.g., using high-resolution mapping) in a singleconfiguration. Thus, such systems can advantageously permit precisehigh-resolution mapping (e.g., to confirm that a desired level oftreatment occurred) during a procedure. In some embodiments, thehigh-resolution tip design that includes two electrodes or electrodeportions 30A, 30B can be used to record a high-resolution bipolarelectrogram. For such purposes, the two electrodes or electrode portionscan be connected to the inputs of an EP recorder. In some embodiments, arelatively small separation distance (e.g., gap G) between theelectrodes or electrode portions 30A, 30B enables high-resolutionmapping.

In some embodiments, a medical instrument (e.g., a catheter) 20 caninclude three or more electrodes or electrode portions (e.g., separatedby gaps), as desired or required. Additional details regarding sucharrangements are provided below. According to some embodiments,regardless of how many electrodes or electrode portions are positionedalong a catheter tip, the electrodes or electrode portions 30A, 30B areradiofrequency electrodes and comprise one or more metals, such as, forexample, stainless steel, platinum, platinum-iridium, gold, gold-platedalloys and/or the like.

According to some embodiments, as illustrated in FIG. 2, the electrodesor electrode portions 30A, 30B are spaced apart from each other (e.g.,longitudinally or axially) using a gap (e.g., an electrically insulatinggap). In some embodiments, the length of the gap G (or the separationdistance between adjacent electrodes or electrode portions) is 0.5 mm.In other embodiments, the gap G or separation distance is greater orsmaller than 0.5 mm, such as, for example, 0.1-1 mm (e.g., 0.1-0.2,0.2-0.3, 0.3-0.4, 0.4-0.5, 0.5-0.6, 0.6-0.7, 0.7-0.8, 0.8-0.9, 0.9-1.0mm, values between the foregoing ranges, less than 0.1 mm, greater than1 mm, etc.), as desired or required.

According to some embodiments, a separator 34 is positioned within thegap G, between the adjacent electrodes or electrode portions 30A, 30B,as depicted in FIG. 2. The separator can comprise one or moreelectrically insulating materials, such as, for example, Teflon,polyetheretherketone (PEEK), polyetherimide resins (e.g., ULTEM™),ceramic materials, polyimide and the like.

As noted above with respect to the gap G separating the adjacentelectrodes or electrode portion, the insulating separator 34 can be 0.5mm long. In other embodiments, the length of the separator 34 can begreater or smaller than 0.5 mm (e.g., 0.1-0.2, 0.2-0.3, 0.3-0.4,0.4-0.5, 0.5-0.6, 0.6-0.7, 0.7-0.8, 0.8-0.9, 0.9-1.0 mm, values betweenthe foregoing ranges, less than 0.1 mm, greater than 1 mm, etc.), asdesired or required.

According to some embodiments, as discussed in greater detail herein, toablate or otherwise heat or treat targeted tissue of a subjectsuccessfully with the high-resolution tip electrode design, such as theone depicted in FIG. 2, the two electrodes or electrode portions 30A,30B are electrically coupled to each other at the RF frequency. Thus,the two electrodes or electrode portions can advantageously function asa single longer electrode at the RF frequency.

FIGS. 3 and 4 illustrate different embodiments of catheter systems 100,200 that incorporate a high-resolution tip design. For example, in FIG.3, the electrode (e.g., radiofrequency electrode) along the distal endof the electrode comprises a first or distal electrode or electrodeportion 110 and a second or proximal electrode or electrode portion 114.As shown and discussed in greater detail herein with reference to otherconfigurations, the high-resolution tip design 100 includes a gap Gbetween the first and second electrodes or electrode portions 110, 114.In some configurations, the second or proximal electrode or electrodeportion 114 is generally longer than the first or distal electrode orelectrode portion 110. For instance, the length of the proximalelectrode 114 can be between 1 to 20 times (e.g., 1-2, 2-3, 3-4, 4-5,5-6, 6-7, 7-8, 8-9, 9-10, 10-11, 11-12, 12-13, 13-14, 14-15, 15-16,16-17, 17-18, 18-19, 19-20, values between the foregoing ranges, etc.)the length of the distal electrode 110, as desired or required. In otherembodiments, the length of the proximal electrode can be greater than 20times (e.g., 20-25, 25-30, more than 30 times, etc.) the length of thedistal electrode. In yet other embodiments, the lengths of the distaland proximal electrodes are about the same. However, in someembodiments, the distal electrode 110 is longer than the proximalelectrode 114 (e.g., by 1 to 20 times, such as, for example, 1-2, 2-3,3-4, 4-5, 5-6, 6-7, 7-8, 8-9, 9-10, 10-11, 11-12, 12-13, 13-14, 14-15,15-16, 16-17, 17-18, 18-19, 19-20, values between the foregoing ranges,etc.).

As shown in FIG. 3 and noted above, regardless of their exact design,relative length diameter, orientation and/or other characteristics, theelectrodes or electrode portions 110, 114 can be separated by a gap G.The gap G can comprise a relatively small electrically insulating gap orspace. In some embodiments, an electrically insulating separator 118 canbe snugly positioned between the first and second electrodes orelectrode portions 110, 114. In certain embodiments, the separator 118can have a length of about 0.5 mm. In other embodiments, however, thelength of the separator 118 can be greater or smaller than 0.5 mm (e.g.,0.1-0.2, 0.2-0.3, 0.3-0.4, 0.4-0.5, 0.5-0.6, 0.6-0.7, 0.7-0.8, 0.8-0.9,0.9-1.0 mm, values between the foregoing ranges, less than 0.1 mm,greater than 1 mm, etc.), as desired or required. The separator caninclude one or more electrically insulating materials (e.g., materialsthat have an electrical conductivity less than about 1000 or less (e.g.,500-600, 600-700, 700-800, 800-900, 900-1000, 1000-1100, 1100-1200,1200-1300, 1300-1400, 1400-1500, values between the foregoing, less than500, greater than 1500, etc.) than the electrical conductivity of metalsor alloys). The separator can comprise one or more electricallyinsulating materials, such as, for example, Teflon, polyetheretherketone(PEEK), polyoxymethylene, acetal resins or polymers and the like.

As shown in FIG. 3, the separator 118 can be cylindrical in shape andcan have the identical or similar diameter and configuration as theadjacent electrodes or electrode portions 110, 114. Thus, in someembodiments, the outer surface formed by the electrodes or electrodeportions 110, 114 and the separator 118 can be generally uniform orsmooth. However, in other embodiments, the shape, size (e.g., diameter)and/or other characteristics of the separator 118 can be different thanone or more of the adjacent electrodes or electrode portions 110, 114,as desired or required for a particular application or use.

FIG. 4 illustrates an embodiment of a system 200 having three or moreelectrodes or electrode portions 210, 212, 214 separated bycorresponding gaps G1, G2. The use of such additional gaps, and thus,additional electrodes or electrode portions 210, 212, 214 that arephysically separated (e.g., by gaps) yet in close proximity to eachother, can provide additional benefits to the high-resolution mappingcapabilities of the system. For example, the use of two (or more) gapscan provide more accurate high-resolution mapping data related to thetissue being treated. Such multiple gaps can provide information aboutthe directionality of cardiac signal propagation. In addition,high-resolution mapping with high-resolution electrode portionsinvolving multiple gaps can provide a more extended view of lesionprogression during the ablation process and higher confidence thatviable tissue strands are not left behind within the targetedtherapeutic volume. In some embodiments, high-resolution electrodes withmultiple gaps can optimize the ratio of mapped tissue surface to ablatedtissue surface. Preferably, such ratio is in the range of 0.2 to 0.8(e.g., 0.2-0.3, 0.3-0.4, 0.4-0.5, 0.5-0.6, 0.6-0.7, 0.7-0.8, ratiosbetween the foregoing, etc.). Although FIG. 4 illustrates an embodimenthaving a total of three electrodes or electrode portions 210, 212, 214(and thus, two gaps G1, G2), a system can be designed or otherwisemodified to comprise additional electrodes or electrode portions, andthus, additional gaps. For example, in some embodiments, an ablation orother treatment system can include 4 or more (e.g., 5, 6, 7, 8, morethan 8, etc.) electrodes or electrode portions (and thus, 3 or moregaps, e.g., 3, 4, 5, 6, 7 gaps, more than 7 gaps, etc.), as desired orrequired. In such configurations, a gap (and/or an electrical separator)can be positioned between adjacent electrodes or electrode portions, inaccordance with the embodiments illustrated in FIGS. 2 to 4.

As depicted in FIGS. 3 and 4, an irrigation tube 120, 220 can be routedwithin an interior of the catheter (not shown for clarity). In someembodiments, the irrigation tube 120, 220 can extend from a proximalportion of the catheter (e.g., where it can be placed in fluidcommunication with a fluid pump) to the distal end of the system. Forexample, in some arrangements, as illustrated in the side views of FIGS.3 and 4, the irrigation tube 120, 220 extends and is in fluidcommunication with one or more fluid ports 211 that extend radiallyoutwardly through the distal electrode 110, 210. Thus, in someembodiments, the treatment system comprises an open irrigation design,wherein saline and/or other fluid is selectively delivered through thecatheter (e.g., within the fluid tube 120, 220) and radially outwardlythrough one or more outlet ports 111, 211 of an electrode 110, 210. Thedelivery of such saline or other fluid can help remove heat away fromthe electrodes and/or the tissue being treated. In some embodiments,such an open irrigation system can help prevent overheating of targetedtissue, especially along the tissue that is contacted by the electrodes.An open irrigation design is also incorporated in the system that isschematically illustrated in FIG. 2. For instance, as depicted in FIG.2, the distal electrode or electrode portion 34 can include a pluralityof outlet ports 36 through which saline or other irrigation fluid canexit.

According to some embodiments, a catheter can include ahigh-resolution-tip electrode design that includes one or more gaps inthe circumferential direction (e.g., radially), either in addition to orin lieu of gaps in the longitudinal direction. One embodiment of asystem 300 comprising one or more electrodes 310A, 310B is illustratedin FIG. 5. As shown, in arrangements where two or more electrodes areincluded, the electrodes 310A, 310B can be longitudinally or axiallyoffset from each other. For example, in some embodiments, the electrodes310A, 310B are located along or near the distal end of a catheter. Insome embodiments, the electrodes 310A, 310B are located along anexterior portion of a catheter or other medical instrument. However, inother configurations, one or more of the electrodes can be positionedalong a different portion of the catheter or other medical instrument(e.g., along at least an interior portion of a catheter), as desired orrequired.

With continued reference to FIG. 5, each electrode 310A, 310B cancomprises two or more sections 320A, 322A and/or 320B, 320B. As shown,in some embodiments, the each section 320A, 322A and/or 320B, 320B canextend half-way around (e.g., 180 degrees) the diameter of the catheter.However, in other embodiments, the circumferential extent of eachsection can be less than 180 degrees. For example, each section canextend between 0 and 180 degrees (e.g., 15, 30, 45, 60, 75, 90, 105, 120degrees, degrees between the foregoing, etc.) around the circumferenceof the catheter along which it is mounted. Thus, in some embodiments, anelectrode can include 2, 3, 4, 5, 6 or more circumferential sections, asdesired or required.

Regardless of how the circumferential electrode sections are designedand oriented, electrically insulating gaps G can be provided betweenadjacent sections to facilitate the ability to use the electrode toconduct high-resolution mapping, in accordance with the variousembodiments disclosed herein. Further, as illustrated in the embodimentof FIG. 5, two or more (e.g., 3, 4, 5, more than 5, etc.) electrodes310A, 310B having two or more circumferential or radial sections can beincluded in a particular system 300, as desired or required.

In alternative embodiments, the various embodiments of a high-resolutiontip design disclosed herein, or variations thereof, can be used with anon-irrigated system or a closed-irrigation system (e.g., one in whichsaline and/or other fluid is circulated through or within one or moreelectrodes to selectively remove heat therefrom). Thus, in somearrangements, a catheter can include two or more irrigation tubes orconduits. For example, one tube or other conduit can be used to deliverfluid toward or near the electrodes, while a second tube or otherconduit can be used to return the fluid in the reverse direction throughthe catheter.

According to some embodiments, a high-resolution tip electrode isdesigned to balance the current load between the various electrodes orelectrode portions. For example, if a treatment system is not carefullyconfigured, the electrical load may be delivered predominantly to one ormore of the electrodes or electrode portions of the high-resolution tipsystem (e.g., the shorter or smaller distal electrode or electrodeportion). This can lead to undesirable uneven heating of the electrode,and thus, uneven heating (e.g., ablation) of the adjacent tissue of thesubject. Thus, in some embodiments, one or more load balancingconfigurations can be used to help ensure that the heating along thevarious electrodes or electrode portions of the system will be generallybalanced. As a result, the high-resolution tip design can advantageouslyfunction more like a longer, single electrode, as opposed to two or moreelectrodes that receive an unequal electrical load (and thus, deliver anunequal amount of heat or level of treatment to the subject's targetedtissue).

One embodiment of a configuration that can be used to balance theelectrical current load delivered to each of the electrodes or electrodeportions in a high-resolution tip design is schematically illustrated inFIG. 6. As shown, one of the electrodes (e.g., the distal electrode) 30Acan be electrically coupled to an energy delivery module 40 (e.g., a RFgenerator). As discussed herein, the module 40 can comprise one or morecomponents or features, such as, for example, an energy generationdevice that is configured to selectively energize and/or otherwiseactivate the energy members (e.g., RF electrodes), one or moreinput/output devices or components, a processor (e.g., a processing orcontrol unit) that is configured to regulate one or more aspects of thetreatment system, a memory and/or the like. Further, such a module canbe configured to be operated manually or automatically, as desired orrequired.

In the embodiment that is schematically depicted in FIG. 6, the distalelectrode 30A is energized using one or more conductors 82 (e.g., wires,cables, etc.). For example, in some arrangements, the exterior of theirrigation tube 38 comprises and/or is otherwise coated with one or moreelectrically conductive materials (e.g., copper, other metal, etc.).Thus, as shown in FIG. 6, the conductor 82 can be placed in contact withsuch a conductive surface or portion of the tube 38 to electricallycouple the electrode or electrode portion 30A to an energy deliverymodule. However, one or more other devices and/or methods of placing theelectrode or electrode portion 30A in electrical communication with anenergy delivery module can be used. For example, one or more wires,cables and/or other conductors can directly or indirectly couple to theelectrodes, without the use of the irrigation tube.

With continued reference to FIG. 6, the first or distal electrode orelectrode portion 30A can be electrically coupled to the second orproximal electrode or electrode portion 30B using one more band-passfiltering elements 84, such as a capacitor, a filter circuit (see, e.g.,FIG. 16), etc. For instance, in some embodiments, the band-passfiltering element 84 comprises a capacitor that electrically couples thetwo electrodes or electrode portions 30A, 30B when radiofrequencycurrent is applied to the system. In one embodiment, the capacitor 84comprises a 100 nF capacitor that introduces a series impedance lowerthan about 3Ω at 500 kHz, which, according to some arrangements, is atarget frequency for RF ablation. However, in other embodiments, thecapacitance of the capacitor(s) or other band-pass filtering elements 84that are incorporated into the system can be greater or less than 100nF, for example, 5 nF to 300 nF, according to the operating RFfrequency, as desired or required. In some embodiments, the capacitanceof the filtering element 84 is selected based on a target impedance at aparticular frequency or frequency range. For example, in someembodiments, the system can be operated at a frequency of 200 kHz to 10MHz (e.g., 200-300, 300-400, 400-500, 500-600, 600-700, 700-800,800-900, 900-1000 kHz, up to 10 MHz or higher frequencies between theforegoing ranges, etc.). Thus, the capacitor that couples adjacentelectrodes or electrode portions to each other can be selected based onthe target impedance for a particular frequency. For example, a 100 nFcapacitor provides about 3Ω of coupling impedance at an operatingablation frequency of 500 kHz.

In some embodiments, a series impedance of 3Ω across the electrodes orelectrode portions 30A, 30B is sufficiently low when compared to theimpedance of the conductor 82 (e.g., wire, cable, etc.), which can beabout 5-10Ω, and the impedance of tissue, which can be about 100Ω, suchthat the resulting tissue heating profile is not negatively impactedwhen the system is in use. Thus, in some embodiments, a filteringelement is selected so that the series impedance across the electrodesor electrode portions is lower than the impedance of the conductor thatsupplies RF energy to the electrodes. For example, in some embodiments,the insertion impedance of the filtering element is 50% of the conductor82 impedance, or lower, or 10% of the equivalent tissue impedance, orlower.

In some embodiments, a filtering element (e.g., capacitor a filtercircuit such as the one described herein with reference to FIG. 16,etc.) can be located at a variety of locations of the device oraccompanying system. For example, in some embodiments, the filteringelement is located on or within a catheter (e.g., near the distal end ofthe catheter, adjacent the electrode, etc.). In other embodiments,however, the filtering element is separate of the catheter. Forinstance, the filtering element can be positioned within or along ahandle to which the catheter is secured, within the generator or otherenergy delivery module, within a separate processor or other computingdevice or component and/or the like).

Similarly, with reference to the schematic of FIG. 7, a filteringelement 384 can be included in an electrode 310 comprisingcircumferentially-arranged portions 320, 322. In FIG. 7, the filteringelement 384 permits the entire electrode 310 to be energized within RFfrequency range (e.g., when the electrode is activated to ablate). Oneor more RF wires or other conductors 344 can be used to deliver power tothe electrode from a generator or source. In addition, separateconductors 340 can be used to electrically couple the electrode 310 formapping purposes.

In embodiments where the high-resolution-tip design (e.g., FIG. 4)comprises three or more electrodes or electrode portions, additionalfiltering elements (e.g., capacitors) can be used to electrically couplethe electrodes or electrode portions to each other. Such capacitors orother filtering elements can be selected to create a generally uniformheating profile along the entire length of the high-resolution tipelectrode. As noted in greater detail herein, for any of the embodimentsdisclosed herein or variations thereof, the filtering element caninclude something other than a capacitor. For example, in somearrangements, the filtering element comprises a LC circuit (e.g., aresonant circuit, a tank circuit, a tuned circuit, etc.). Suchembodiments can be configured to permit simultaneous application of RFenergy and measurement of EGM recordings.

As discussed above, the relatively small gap G between the adjacentelectrodes or electrode portions 30A, 30B can be used to facilitatehigh-resolution mapping of the targeted tissue. For example, withcontinued reference to the schematic of FIG. 6, the separate electrodesor electrode portions 30A, 30B can be used to generate an electrogramthat accurately reflects the localized electrical potential of thetissue being treated. Thus, a physician or other practitioner using thetreatment system can more accurately detect the impact of the energydelivery to the targeted tissue before, during and/or after a procedure.For example, the more accurate electrogram data that result from suchconfigurations can enable the physician to detect any gaps or portionsof the targeted anatomical region that was not properly ablated orotherwise treated. Specifically, the use of a high-resolution tip designcan enable a cardiac electrophysiologist to more accurately evaluate themorphology of resulting electrograms, their amplitude and width and/orto determine pacing thresholds. In some embodiments, morphology,amplitude and pacing threshold are accepted and reliable EP markers thatprovide useful information about the outcome of an ablation or otherheat treatment procedure.

According to some arrangements, the high-resolution-tip electrodeembodiments disclosed herein are configured to provide localizedhigh-resolution electrogram. For example, the electrogram that isobtained using a high-resolution-tip electrode, in accordance withembodiments disclosed herein, can provide electrogram data (e.g.,graphical output) 400 a, 400 b as illustrated in FIG. 8. As depicted inFIG. 8, the localized electrograms 400 a, 400 b generated using thehigh-resolution-tip electrode embodiments disclosed herein include anamplitude A1, A2.

With continued reference to FIG. 8, the amplitude of the electrograms400 a, 400 b obtained using high-resolution-tip electrode systems can beused to determine whether targeted tissue adjacent thehigh-resolution-tip electrode has been adequately ablated or otherwisetreated. For example, according to some embodiments, the amplitude A1 ofan electrogram 400 a in untreated tissue (e.g., tissue that has not beenablated or otherwise heated) is greater that the amplitude A2 of anelectrogram 400 b that has already been ablated or otherwise treated. Insome embodiments, therefore, the amplitude of the electrogram can bemeasured to determine whether tissue has been treated. For example, theelectrogram amplitude A1 of untreated tissue in a subject can berecorded and used as a baseline. Future electrogram amplitudemeasurements can be obtained and compared against such a baselineamplitude in an effort to determine whether tissue has been ablated orotherwise treated to an adequate or desired degree.

In some embodiments, a comparison is made between such a baselineamplitude (A1) relative to an electrogram amplitude (A2) at a tissuelocation being tested or evaluated. A ratio of A1 to A2 can be used toprovide a quantitative measure for assessing the likelihood thatablation has been completed. In some arrangements, if the ratio (i.e.,A1/A2) is above a certain minimum threshold, then the user can beinformed that the tissue where the A2 amplitude was obtained has beenproperly ablated. For example, in some embodiments, adequate ablation ortreatment can be confirmed when the A1/A2 ratio is greater than 1.5(e.g., 1.5-1.6, 1.6-1.7, 1.7-1.8, 1.8-1.9, 1.9-2.0, 2.0-2.5, 2.5-3.0,values between the foregoing, greater than 3, etc.). However, in otherembodiments, confirmation of ablation can be obtained when the ratio ofA1/A2 is less than 1.5 (e.g., 1-1.1, 1.1-1.2, 1.2-1.3, 1.3-1.4, 1.4-1.5,values between the foregoing, etc.).

For any of the embodiments disclosed herein, a catheter or otherminimally-invasive medical instrument can be delivered to the targetanatomical location of a subject (e.g., atrium, pulmonary veins, othercardiac location, renal artery, other vessel or lumen, etc.) using oneor more imaging technologies. Accordingly, any of the ablation systemsdisclosed herein can be configured to be used with (e.g., separatelyfrom or at least partially integrated with) an imaging device or system,such as, for example, fluoroscopy technologies, intracardiacechocardiography (ICE) technologies and/or the like.

Thermal Shunting

FIG. 9 illustrates one embodiment of a system 1100 comprising anelectrode 1130 (e.g., a unitary RF electrode, a split-tip electrodehaving two, three or more portions, other types of electrodes, etc.)located at or near the distal end of a catheter 1120. In addition, aswith any other embodiments disclosed herein, the system can furtherinclude a plurality of ring electrodes 1170 to assist with the executionof a treatment procedure (e.g., mapping of tissue adjacent the treatmentsite, monitoring of the subject, etc.). Although the embodiments of thevarious systems and related methods disclosed herein are described inthe context of radiofrequency (RF) based ablation, the heat transferconcepts (including heat shunting embodiments), either alone or inconjunction with other embodiments described herein (e.g., split-tipconcepts, temperature sensing concepts, etc.), can be implemented inother types of ablation systems as well, such as those, for example,that use microwave emitters, ultrasound transducers, cryoablationmembers and/or the like to target tissue of a subject.

With reference to FIG. 9 and the corresponding partially-exposed view ofthe distal end of the catheter illustrated in FIG. 10, one or more heattransfer members or other heat transfer components or features,including any of the heat shunting embodiments disclosed herein, can beused to facilitate the heat transfer from or near the electrode to theirrigation conduit 1108 that extends through the interior of thecatheter 1120. For example, in some embodiments, as depicted in FIG. 10,one or more heat transfer disks or members 1140 (e.g., heat shunt disksor members) can be positioned along the length of the electrode 1130. Insome arrangements, the disks or other heat transfer members 1140(including any of the heat shunting embodiments disclosed herein)comprise separate components that may or may not contact each other. Inother embodiments, however, the heat transfer disks or other heattransfer members 1140 comprise a unitary or monolithic structure, asdesired or required. The disks 1140 can be in direct or indirect thermalcommunication with the irrigation conduit 1108 that passes, at leastpartially, through an interior portion (e.g., along the longitudinalcenterline) of the catheter. For example, the disks 1140 can extend toand make contact with an exterior surface of the irrigation conduitand/or another interior portion of the catheter (e.g., non-irrigationcomponent or portion for embodiments that do not include active coolingusing open or closed irrigation). However, in other embodiments, asillustrated in FIG. 11, the disks 1140 can be in thermal communication(e.g., directly via contact or indirectly) with one or more other heatexchange components or members, including any heat shunting componentsor members, located between the disks and the irrigation conduit.

A heat sink includes both (i) a heat retention transfer in which heat islocalized to/retained by a certain component, and (ii) a heat shunt(which can also be called a heat transfer member) that is used to shuntor transfer heat from, e.g., an electrode to an irrigation passageway.In one embodiment, a heat retention sink is used to retain heat for someperiod of time. Preferably, a heat shunt (heat transfer member) is usedrather than a heat retention sink. A heat shunt (heat transfer member),in some embodiments, provides more efficient dissipation of heat andimproved cooling, thus, for example, offering a protective effect totissue that is considered non-target tissue. For any of the embodimentsdisclosed herein, one or more heat shunting components can be used toeffectively and safely transfer heat away from an electrode and/or thetissue being heated. In some embodiments, a device or system can beconfigured to adequately transfer heat away from the electrode withoutany additional components or features (e.g., solely using the heatshunting configurations disclosed herein).

In any of the embodiments disclosed herein, the ablation system caninclude one or more irrigation conduits that extend at least partiallyalong (e.g., through an interior portion of) a catheter or other medicalinstrument configured for placement within a subject. The irrigationconduit(s) can be part of an open irrigation system, in which fluidexits through one or more exit ports or openings along the distal end ofthe catheter (e.g., at or near the electrode) to cool the electrodeand/or the adjacent targeted tissue. Alternatively, however, theirrigation conduit(s) can be part of a closed irrigation system, inwhich irrigation fluid is circulated at least partially through (e.g.,as opposed to being expelled from) the catheter (e.g., in the vicinityof the electrode or other ablation member to selectively cool theelectrode and/or the adjacent tissue of the subject. For example, insome arrangements, the catheter comprises at least two internal fluidconduits (e.g., a delivery conduit and a return conduit) to circulateirrigation fluid to and perform the desired or necessary heat transferwith the distal end of the catheter, as desired or required. Further, insome embodiments, in order to facilitate the heat transfer between theheat transfer members or components included in the ablation system(e.g., heat shunting members or components), the system can comprise anirrigation conduit that comprises one or more metallic and/or otherfavorable heat transfer materials (e.g., copper, stainless steel, othermetals or alloys, ceramics, polymeric and/or other materials withrelatively favorable heat transfer properties, etc.). In yet otherembodiments, the catheter or other medical instrument of the ablationsystem does not include any active fluid cooling system (e.g., open orclosed irrigation passage or other components extending through it), asdesired or required. As discussed in greater detail herein, suchembodiments that do not include active cooling using fluid passagethrough the catheter can take advantage of enhanced heat transfercomponents and/or designs to advantageously dissipate and/or distributeheat away from the electrode(s) and/or the tissue being treated.

In some embodiments, the irrigation conduit is fluid communication onlywith exit ports located along the distal end of the elongate body. Insome embodiments, the catheter only comprises irrigation exit openingsalong a distal end of the catheter (e.g., along a distal end or theelectrode). In some embodiments, the system does not comprise anyirrigation openings along the heat transfer members (e.g., heat shuntmembers), and/or, as discussed herein, the system does not comprise anactive irrigation system at all. Thus, in such embodiments, the use ofheat transfer members along the catheter (e.g., at or near the electrodeor other ablation member) help more evenly distribute the heat generatedby the electrode or other ablation member and/or assist in heat transferwith the surrounding environment (e.g., blood or other fluid passingalong an exterior of the ablation member and/or catheter).

With continued reference to FIG. 10, the proximal end 1132 of theelectrode 1130 comprises one or more additional heat transfer members1150, including any heat shunt embodiments disclosed herein. Forexample, according to some embodiments, such additional heat transfermembers 1150 (e.g., heat shunt members) comprise one or more fins, pinsand/or other members that are in thermal communication with theirrigation conduit 108 extending through an interior of the catheter ofthe system. Accordingly, as with the heat transfer disks or other heattransfer members 1140 positioned along the length of the electrode 1130,including heat shunting members, heat can be transferred and thusremoved, from the electrode, the adjacent portions of the catheterand/or the adjacent tissue of the subject, when the electrode isactivated, via these heat transfer members 1150.

In any of the embodiments disclosed herein or variations thereof, theheat transfer members 1140, 1150 of the system 1100 that are placed inthermal communication with the irrigation conduit 1108 can comprise oneor more materials that include favorable heat transfer properties,including, but not limited to, favorable heat shunting properties. Forexample, in some embodiments, the thermal conductivity of thematerial(s) included in the heat transfer members and/or of the overallheat transfer assembly (e.g., when viewed as a unitary member orstructure) is greater than 300 W/m/° C. (e.g., 300-350, 350-400,400-450, 450-500, 500-600, 600-700 W/m/° C., ranges between theforegoing, greater than 700 W/m/° C., etc. Possible materials withfavorable thermal conductivity properties include, but are not limitedto, copper, brass, beryllium, other metals and/or alloys, aluminalceramics, other ceramics, industrial diamond and/or other metallicand/or non-metallic materials.

According to certain embodiments where the heat transfer memberscomprise heat shunting members, the thermal diffusivity of thematerial(s) included in the heat shunt members and/or of the overallheat shunt assembly (e.g., when viewed as a unitary member or structure)is greater than 1.5 cm²/sec (e.g., 1.5-2, 2-2.5, 2.5-3, 3-4, 4-5, 5-6,6-7, 7-8, 8-9, 9-10, 10-11, 11-12, 12-13, 13-14, 14-15, 15-20 cm²/sec,values between the foregoing ranges, greater than 20 cm²/sec). Thermaldiffusivity measures the ability of a material to conduct thermal energyrelative to its ability to store thermal energy. Thus, even though amaterial can be efficient as transferring heat (e.g., can have arelatively high thermal conductivity), it may not have favorable thermaldiffusivity properties, because of its heat storage properties. Heatshunting, unlike heat transferring, requires the use of materials thatpossess high thermal conductance properties (e.g., to quickly transferheat through a mass or volume) and a low heat capacity (e.g., to notstore heat). Possible materials with favorable thermal diffusivity, andthus favorable heat shunting properties, include, but are not limitedto, industrial diamond, Graphene, silica, other carbon-based materialsand/or the like.

The use of materials with favorable thermal diffusivity properties canhelp ensure that heat can be efficiently transferred away from theelectrode and/or the adjacent tissue during a treatment procedure. Incontrast, materials that have favorable thermal conductivity properties,but not favorable thermal diffusivity properties, such as, e.g., copper,other metals or alloys, thermally conductive polypropylene or otherpolymers, etc., will tend to retain heat. As a result, the use of suchmaterials that store heat may cause the temperature along the electrodeand/or the tissue being treated to be maintained at an undesirablyelevated level (e.g., over 75 degrees C.) especially over the course ofa relatively long ablation procedure, which may result in charring,thrombus formation and/or other heat-related problems.

Industrial diamond and other materials with the requisite thermaldiffusivity properties for use in a thermal shunting network, asdisclosed in the various embodiments herein, comprise favorable thermalconduction characteristics. Such favorable thermal conduction aspectsemanate from a relatively high thermal conductance value (k) and themanner in which the heat shunt members of a network are arranged withrespect to each other within the tip and with respect to the tissue. Forexample, in some embodiments, as RF energy is emitted from the tip andthe ohmic heating within the tissue generates heat, the exposed distalmost shunt member (e.g., located 0.5 mm from the distal most end of thetip) can actively extract heat from the lesion site. The thermal energycan advantageously transfer through the shunting network in a relativelyrapid manner and dissipate through the shunt residing beneath the RFelectrode surface the heat shunt network, through a proximal shuntmember and/or into the ambient surroundings. Heat that is shuntingthrough an interior shunt member can be quickly transferred to anirrigation conduit extending through an interior of the catheter orother medical instrument. In other embodiments, heat generated by anablation procedure can be shunted through both proximal and distal shuntmembers (e.g., shunt members that are exposed to an exterior of thecatheter or other medical instrument, such as shown in many of theembodiments herein).

Further, as noted above, the materials with favorable thermaldiffusivity properties for use in a heat shunt network not only have therequisite thermal conductivity properties but also have sufficiently lowheat capacity values (c). This helps ensure that the thermal energy isdissipated very quickly from the tip to tissue interface as well as thehot spots on the electrode, without heat retention in the heat shuntingnetwork. The thermal conduction constitutes the primary heat dissipationmechanism that ensures quick and efficient cooling of the tissue surfaceand of the RF electrode surface. Conversely a heat transfer (e.g., withrelatively high thermal conductivity characteristics but also relativelyhigh heat capacity characteristics) will store thermal energy. Over thecourse of a long ablation procedure, such stored heat may exceed 75degrees C. Under such circumstances, thrombus and/or char formation canundesirably occur.

The thermal convection aspects of the various embodiments disclosedherein two-fold. First, an irrigation lumen of the catheter can absorbthermal energy which is transferred to it through the shunt network.Such thermal energy can then be flushed out of the distal end of the RFtip via the irrigation ports. In closed irrigation systems, however,such thermal energy can be transferred back to a proximal end of thecatheter where it can be removed. Second, the exposed shunt surfacesalong an exterior of the catheter or other medical instrument canfurther assist with the dissipation of heat from the electrode and/orthe tissue being treated. For example, such heat dissipation can beaccomplished via the inherent convective cooling aspects of the bloodflowing over the surfaces of the electrode.

Accordingly, the use of materials in a heat shunting network withfavorable thermal diffusivity properties, such as industrial diamond,can help ensure that heat is quickly and efficiently transferred awayfrom the electrode and treated tissue, while maintaining the heatshunting network cool (e.g., due to its low heat capacity properties).This can create a safer ablation catheter and related treatment method,as potentially dangerous heat will not be introduced into the procedurevia the heat shunting network itself.

For example, in some embodiments, during the course of an ablationprocedure that attempts to maintain the subject's tissue at a desiredtemperature of about 60 degrees C., the temperature of the electrode isapproximately 60 degrees Celsius. Further, the temperature oftraditional heat transferring members positioned adjacent the electrode(e.g., copper, other metals or alloys, thermally-conductive polymers,etc.) during the procedure is approximately 70 to 75 degrees Celsius. Incontrast, the temperature of the various portions or members of the heatshunting network for systems disclosed herein can be approximately 60 to62 degrees Celsius (e.g., 10% to 30% less than comparable heattransferring systems) for the same desired level of treatment of tissue.

In some embodiments, the heat shunt members disclosed herein draw outheat from the tissue being ablated and shunt it into the irrigationchannel. Similarly, heat is drawn away from the potential hot spots thatform at the edges of RF electrodes and are shunted through the heatshunt network into the irrigation channel. From the irrigation channel,via convective cooling, heat can be advantageously released into theblood stream and dissipated away. In closed irrigation systems, heat canbe removed from the system without expelling irrigation fluid into thesubject.

According to some embodiments, the various heat shunting systemsdisclosed herein rely on heat conduction as the primary coolingmechanism. Therefore, such embodiments do not require a vast majority ofthe heat shunting network to extend to an external surface of thecatheter or other medical instrument (e.g., for direct exposure to bloodflow). In fact, in some embodiments, the entire shunt network can residewithin an interior of the catheter tip (i.e., with no portion of theheat shut network extending to an exterior of the catheter or othermedical instrument). Further, the various embodiments disclosed hereindo not require electrical isolation of the heat shunts from the RFelectrode or from the irrigation channel.

According to some embodiments, the heat transfer disks and/or other heattransfer members 1140, 1150 included in a particular system, includingheat shunting members or components, can continuously and/orintermittently or partially extend to the irrigation conduit 108, asdesired or required for a particular design or configuration. Forinstance, as illustrated in the embodiment of FIG. 10, the proximal heattransfer member 1150 (e.g., heat shunt members) can comprise one or more(e.g., 2, 3, 4, 5, more than 5, etc.) wings or portions 1154 than extendradially outwardly from a base or inner member 1152. In someembodiments, such wings or radially-extending portion 1154 are equallyspaced from each other to more evenly transfer heat toward theirrigation conduit 1108 with which the heat transfer member 1150 is inthermal communication. Alternatively, however, the heat transfer member1150, including, but not limited to, a heat shunt member, can include agenerally solid or continuous structure between the irrigation conduit1108 and a radially exterior portion or region of the catheter.

According to some embodiments, heat transfer members (e.g., fins) 1150can extend proximally to the proximal end of the electrode(s) includedalong the distal end of a catheter. For example, as illustrated in FIG.10, the heat transfer members 1150 (e.g., heat shunt members) can extendto, near or beyond the proximal end of the electrode 1130. In someembodiments, the heat transfer members 1150 terminate at or near theproximal end 1132 of the electrode 1130. However, in other arrangements,the heat transfer members 1150, including, without limitation, heatshunt members, extend beyond the proximal end 1132 of the electrode1130, and in some embodiments, contact and/or are otherwise in direct orindirect thermal communication with distally-located heat transfermembers (e.g., heat transfer disks or other heat transfer memberslocated along or near the length of the electrode 1130), including heatshunt members, as desired or required. In yet other embodiments,proximal heat transfer members (e.g., heat shunt members) terminateproximally to the proximal end 1132 of the electrode or other ablationmember.

In any of the embodiments disclosed herein, including the systemscomprising the enhanced heat transfer (e.g., heat shunting) propertiesdiscussed in connection with FIGS. 9-12, the system can include one ormore temperature sensors or temperature detection components (e.g.,thermocouples) for the detection of tissue temperature at a depth. Forexample, in the embodiments illustrated in FIGS. 9 and 10, the electrodeand/or other portion of the distal end of the catheter can include oneor more sensors (e.g., thermocouples, thermistors, etc.) and/or thelike. Thus, signals received by sensors and/or othertemperature-measurement components can be advantageously used todetermine or approximate the extent to which the targeted tissue isbeing treated (e.g., heated, cooled, etc.). Temperature measurements canbe used to control an ablation procedure (e.g., module power provided tothe ablation member, terminate an ablation procedure, etc.), inaccordance with a desired or required protocol.

In some embodiments, the device further comprises a one or moretemperature sensors or other temperature-measuring devices to helpdetermine a peak (e.g., high or peak, low or trough, etc.) temperatureof tissue being treated. In some embodiments, the temperature sensors(e.g., thermocouples) located at, along and/or near the ablation member(e.g., RF electrode) can help with the determination of whether contactis being made between the ablation member and targeted tissue (and/or towhat degree such contact is being made). In some embodiments, such peaktemperature is determined without the use of radiometry. Additionaldetails regarding the use of temperature sensors (e.g., thermocouples)to determine peak tissue temperature and/or to confirm or evaluatetissue contact are provided herein.

In some embodiments, for any of the systems disclosed herein (includingbut not limited to those illustrated herein) or variations thereof, oneor more of the heat transfer members, including, but not limited to,heat shunt members, that facilitate the heat transfer to an irrigationconduit of the catheter are in direct contact with the electrode and/orthe irrigation conduit. However, in other embodiments, one or more ofthe heat transfer members (e.g., heat shunt members) do not contact theelectrode and/or the irrigation conduit. Thus, in such embodiments, theheat transfer members are in thermal communication with the electrodeand/or irrigation conduit, but not in physical contact with suchcomponents. For example, in some embodiments, one or more intermediatecomponents, layers, coatings and/or other members are positioned betweena heat transfer member (e.g., a heat shunt member) and the electrode (orother ablation member) and/or the irrigation conduit.

FIG. 11 illustrates another embodiment of an ablation system 1200comprising an electrode (e.g., a RF electrode, a split-tip electrode,etc.) or other ablation member 1230 located along or near the distal endof a catheter or other elongated member. In some embodiments, aninterior portion 1236 of the electrode or other ablation member (notshown in FIG. 11, for clarity) can include a separate, internal heattransfer member 1250B, including any heat shunt embodiments disclosedherein. Such a heat transfer member 1250B can be in addition to or inlieu of any other heat transfer members located at, within and/or nearthe electrode or other ablation member. For example, in the depictedembodiment, in the vicinity of the electrode 1230, the system 1200comprises both an internal heat transfer member 1250B and one or moredisk-shaped or cylindrical heat transfer members 1240 (e.g., heatshunting members).

For any of the embodiments disclosed herein, at least a portion of heattransfer member, including a heat shunt member, that is in thermalcommunication with the irrigation conduit extends to an exterior surfaceof the catheter, adjacent to (and, in some embodiments, in physicaland/or thermal contact with) the electrode or other ablation member.Such a configuration, can further enhance the cooling of the electrodeor other ablation member when the system is activated, especially at ornear the proximal end of the electrode or ablation member, where heatmay otherwise tend to be more concentrated (e.g., relative to otherportions of the electrode or other ablation member). According to someembodiments, thermal conductive grease and/or any other thermallyconductive material (e.g., thermally-conductive liquid or other fluid,layer, member, coating and/or portion) can be used to place the thermaltransfer, such as, for example, a heat shunt member or heat shuntnetwork, in thermal communication with the irrigation conduit, asdesired or required. In such embodiments, such a thermally conductivematerial places the electrode in thermal communication, at leastpartially, with the irrigation conduit.

With continued reference to FIG. 11, the heat transfer member (e.g.,heat shunt member) 1250B located along an interior portion of theelectrode 1230 can include one or more fins, wings, pins and/or otherextension members 1254B. Such members 1254B can help enhance heattransfer with the (e.g., heat shunting to, for heat shuntingembodiments) irrigation conduit 1208, can help reduce the overall sizeof the heat transfer member 1254B and/or provide one or more additionaladvantages or benefits to the system 1200.

Another embodiment of an ablation system 1300 comprising one or moreheat transfer (e.g., heat shunt) components or features that facilitatethe overall heat transfer of the electrode or other ablation memberduring use is illustrated in FIG. 12. As shown, heat transfer (e.g.,shunting) between one or more heat transfer members 1350B located alongan interior of an electrode or other ablation member 1330 can befacilitated and otherwise enhanced by eliminating air gaps or othersimilar spaces between the electrode and the heat transfer members. Forexample, in the illustrated embodiment, one or more layers 1356 of anelectrically conductive material (e.g., platinum, gold, other metals oralloys, etc.) have been positioned between the interior of the electrode1330 and the exterior of the heat transfer member 1350B. Such layer(s)1356 can be continuously or intermittently applied between the electrode(or another type of ablation member or energy delivery member) and theadjacent heat transfer member(s), including, but not limited to, heatshunting member(s). Further, such layer(s) 1356 can be applied using oneor more methods or procedures, such as, for example, sputtering, otherplating techniques and/or the like. Such layer(s) 1356 can be used inany of the embodiments disclosed herein or variations thereof.

FIG. 13 illustrates a distal portion of a catheter or other medicalinstrument of an ablation system 1800 comprising one or more heattransfer members 1850 (e.g., heat shunt members) that facilitate theefficient transfer of heat generated by the electrode or other energydelivery member 1830. As shown in FIG. 13, the heat shunt members 1850are positioned immediately adjacent (e.g., within an interior of) theelectrode 1830. Accordingly, as discussed in greater detail herein, heatgenerated by the electrode or other energy delivery member 1830 can betransferred via the one or more heat shunt members 1850. As discussedabove, the heat shunt members advantageously comprise favorable thermaldiffusivity properties to quickly transfer heat while not retainingheat. Thus, the likelihood of localized hot spots (e.g., along thedistal and/or proximal ends of the electrode) can be prevented orreduced. In addition, the heat dissipation or removal (e.g., away fromthe electrode) can be more easily and/or quickly realized using the heatshunt members 1850.

As discussed herein, for example, the heat shunt members 1850 caninclude industrial diamond, Graphene, silica or other carbon-basedmaterials with favorable thermal diffusivity properties and/or the like.In some embodiments, the heat shunt members 1850 comprise a combinationof two, three or more materials and/or portions, components or members.In some embodiments, the thermal diffusivity of the material(s) includedin the heat shunt members and/or of the overall heat shunting network orassembly (e.g., when viewed as a unitary member or structure) is greaterthan 1.5 cm²/sec (e.g., 1.5-2, 2-2.5, 2.5-3, 3-4, 4-5, 5-6, 6-7, 7-8,8-9, 9-10, 10-11, 11-12, 12-13, 13-14, 14-15, 15-20 cm²/sec, valuesbetween the foregoing ranges, greater than 20 cm²/sec).

The heat shunt members 1850 (e.g., fins, rings, blocks, etc.) can be indirect or indirect contact with the electrode or other energy deliverymember 1830. Regardless of whether direct physical contact is madebetween the electrode and one or more of the heat transfer shunt 1850,the heat shunt members 1850 can be advantageously in thermalcommunication with the electrode, thereby facilitating the heatdissipation and/or heat transfer properties of the catheter or othermedical instrument. In some embodiments, for example, one or moreintermediate layers, coatings, members and/or other components arepositioned between the electrode (or other energy delivery member) andthe heat shunt members, as desired or required.

With continued reference to FIG. 13, as discussed with other embodimentherein, a catheter or other medical instrument of the ablation system1800 comprises an open irrigation system configured to deliver a coolingfluid (e.g., saline) to and through the distal end of the catheter orother medical instrument. Such an open irrigation system can help removeheat from the electrode or other energy delivery member during use. Insome embodiments, the heat shunting network and the favorable thermaldiffusivity properties it possesses can help to quickly and efficientlytransfer heat from the electrode and/or the tissue being treated to anirrigation conduit or passage 1804 or chamber 1820 during use. Forexample, as depicted in FIG. 13, an irrigation conduit or passage 1804extends through an interior of the catheter and is in fluidcommunication with one or more outlet ports 1811 along the distal member1810 of the catheter. However, as discussed in greater detail herein,enhanced heat shunt members can be incorporated into the design of acatheter or other medical instrument without the use of an openirrigation system and/or without an active fluid cooling system, asdesired or required. In some embodiments, the flow of irrigation fluid(e.g., saline) through the irrigation conduit or chamber of the catheteror other medical instrument can be modified to vary the heat shuntingthat occurs through the heat shunting network. For example, in someembodiments, due to the favorable heat transfer properties of the heatshunting network and its ability to not retain heat, the flow rate ofirrigation fluid through a catheter can be maintained below 5 ml/min(e.g., 1-2, 2-3, 3-4, 4-5 ml/min, flow rates between the foregoingranges, less than 1 ml/min, etc.). In one embodiment, the flow rate ofirrigation fluid through a catheter is maintained at approximately 1ml/min. In other embodiments, the flow rate of irrigation fluid passingthrough the catheter can be between 5 and 15 ml/min (e.g., 5-6, 6-7,7-8, 8-9, 9-10, 11-12, 12-13, 13-14, 14-15 ml/min, flow rates betweenthe foregoing rates, etc.) or greater than 15 ml/min (e.g., 15-16,16-17, 17-18, 18-19, 19-20 ml/min, flow rates between the foregoingrates, etc.), as desired or required. In some embodiments, suchirrigation flow rates are significantly less than would otherwise berequired if non-heat shunting members (e.g., metals, alloys,thermally-conductive polymers, other traditional heat transferringmembers, etc.) were being used to transfer heat away from the electrodeand/or the tissue between treated. For example, the required flow rateof the irrigation fluid passing through an interior of a catheter thathas a heat shunting member in accordance with the various embodimentsdisclosed herein or variations thereof, can be decreased by 20% to 90%(e.g., 20-25, 25-30, 30-35, 35-40, 40-45, 45-50, 50-55, 55-60, 60-65,65-70, 70-75, 75-80, 80-85, 85-90%, percentages between the foregoingranges, etc.), as compared to systems that use traditional heattransferring members or no heat transferring members at all (e.g.,assuming the same amount of heating is produced at the electrode, thesame anatomical location is being treated and other parameters are thesame). For example, in some commercially available RF ablation systems,an irrigation flow rate of about 30 ml/min (e.g., 25-35 ml/min) istypically required to accomplish a desired level of heat transfer wayfrom the electrode. As noted above, in some arrangements, the systemsdisclosed herein that utilize a heat shunting network can utilize airrigation flow rate of about 10 ml/min or lower to effectively shuntthe heat away from the electrode. Thus, in such embodiments, theirrigation flow rate can be reduced by at least 60% to 70% relative totraditional and other commercially available systems.

Thus, as noted in greater detail herein, the use of heat shuntingmaterials to shunt heat away from the electrode and/or the adjacenttissue can also reduce the amount of irrigation fluid that is beingdischarged into the subject's blood stream in an open irrigation system.Since the discharge of irrigation fluid into the subject is notdesirable, the use of heat shunting in an ablation catheter can provideadditional benefits to an ablation procedure. For example, in somearrangements, discharging excessive saline or other cooling fluid intothe heart, blood vessel and/or other targeted region of the subject canbring about negative physiological consequences to the subject (e.g.,heart failure).

As noted above, the use of heat shunting components at or near theelectrode can also provide one or more additional benefits andadvantages. For example, a significantly lower irrigation flow rate isrequired to effectively remove heat away from the electrode and thesurrounding tissue using heat shunting components (e.g., vis-à-vistraditional heat transferring components and members), the irrigationfluid in such systems is less likely to negatively impact anytemperature sensors that are located along or near the outside of thedistal end of a catheter, allowing more accurate temperaturemeasurements. This is particularly relevant for systems, such as thosedisclosed herein, where temperature sensors are configured to detect thetemperature of adjacent tissue of a subject (e.g., not the temperatureof the electrode or another component or portion of the treatmentsystem). Thus, the lower volume of fluid being discharged at or in thevicinity of the sensors (e.g., compared to systems that do not use heatshunting, systems that include traditional heat transfer components,systems that rely primarily or strictly on heat transfer between theelectrode (and/or tissue) and blood passing adjacent the electrode(and/or tissue), other open-irrigation systems, etc.) can increase theaccuracy of the temperature measurements obtained by the sensors locatedat or near the distal end of a catheter or other medical instrument.

Also, since the irrigation fluid can be delivered at a lower flow ratewhich is characterized by a laminar flow profile (e.g., as opposed to aturbulent flow profile that may be required when the irrigation flowrate is higher), any disruptive fluid dynamic effects resulting from anotherwise higher flow rate can be advantageously avoided or at leastreduced. Thus, the laminar flow of fluid (and/or in conjunction with thesignificantly lower flow rate of the fluid relative to higher flowsystems) can help with the accuracy of the temperature measurements bythe sensors located near the electrode, the tissue being treated and/orany other location along the distal end of the catheter or other medicalinstrument.

Further, since heat shunting components positioned along or near theelectrode are so effective in transferring heat away from the electrodeand/or the adjacent tissue of the subject being treated withoutretaining the heat being transferred, the need to have a longerelectrode and/or larger heat transferring members or portions can beadvantageously eliminated. For example, traditional systems that utilizeone or more heat transferring members (as opposed and in contrast toheat shunting members) or systems that do not use any heat transferringmembers or components at all rely on the heat transfer between theelectrode and the surrounding environment (e.g., blood that flows pastthe electrode, irrigation fluid passing through an interior of thecatheter, etc.) to attempt to cool the electrode. As a result, thelength, size and/or other dimensions of the electrode or traditionalheat transferring members needs to be increased. This is done toincrease the surface area for improved heat transfer between theelectrode and/or the heat transferring members and the fluid that willprovide the heat transfer (e.g., blood, irrigation fluid, etc.).However, in various embodiments disclosed herein, it is advantageouslynot necessary to provide such enlarged surface areas for the electrodeand/or the heat shunting components or other members of the heatshunting network. Accordingly, the electrode can be sized based on theintended ablation/heating and/or mapping (e.g., high-resolution)properties without the need to oversize based on heat transfer capacity.Such oversizing can negatively impact the safety and efficacy of alesion formation procedure.

Therefore, as discussed herein, in some embodiments, the size of theheat shunting members can be advantageously reduced (e.g., as comparedto the size of heat transferring members in traditional systems). Heatgenerated during a treatment procedure can be efficiently and rapidlytransferred away from electrode and/or the tissue being treated via theheat shunting network without the fear of such network retaining theheat being transferred. In some embodiments, the heat can be shunted toirrigation fluid passing through an interior of the catheter or othermedical instrument. In other embodiments, heat can be transferred tosurrounding bodily fluid of the subject (e.g., blood) via heat shuntingmembers that are positioned along an exterior of the catheter or othermedical instrument, either in addition or in lieu of heat shunting to anirrigation fluid.

According to some embodiments, the total length (e.g., along alongitudinal direction) of the heat shunting members that extend to theexterior of the catheter or other medical instrument (such as, e.g., inthe configurations depicted in FIGS. 13 to 17B) can be 1 to 3 mm (e.g.,1-1.5, 1.5-2, 2-2.5, 2.5-3 mm, lengths between the foregoing values,etc.). As noted above, despite such a relatively short exposure length,the heat shunting members can effectively transfer heat away from theelectrode and/or the tissue being ablated without retaining heat.

According to some embodiments, the total length (e.g., along alongitudinal direction) of the heat shunting members that extend alongan interior of the catheter or other medical instrument (such as, e.g.,in the configurations depicted in FIGS. 13 to 17B) can be 1 to 30 mm(e.g., 1-2, 2-3, 3-4, 4-5, 5-6, 6-7, 7-8, 8-9, 9-10, 10-11, 11-12,12-13, 13-14, 14-15, 15-20, 20-25, 25-30 mm, lengths between theforegoing values, etc.). As noted above, despite such a relatively shortoverall length, the heat shunting members can effectively transfer heataway from the electrode and/or the tissue being ablated to fluid passingthrough the irrigation channel of the catheter or other medicalinstrument without retaining heat.

According to some embodiments, the total length (e.g., along alongitudinal direction) of the heat shunting members that extend alongan interior of the catheter or other medical instrument plus theelectrode (such as, e.g., in the configurations depicted in FIGS. 13 to17B) can be 1 to 30 mm (e.g., 1-2, 2-3, 3-4, 4-5, 5-6, 6-7, 7-8, 8-9,9-10, 10-11, 11-12, 12-13, 13-14, 14-15, 15-20, 20-25, 25-30 mm, lengthsbetween the foregoing values, etc.). As noted above, despite such arelatively short overall length, the heat shunting members caneffectively transfer heat away from the electrode and/or the tissuebeing ablated to fluid passing through the irrigation channel of thecatheter or other medical instrument without retaining heat.

As illustrated in FIG. 13, an interior of the distal end of the catheteror other medical instrument can comprise a cooling chamber or region1820 that is in fluid communication with the irrigation conduit orpassage 1804. As shown, according to some embodiments, the coolingchamber 1820 includes a diameter or cross-sectional dimension that isgreater than the diameter or cross-sectional dimension of the fluidconduit or passage 1804. For example, in some arrangements, the diameteror other cross-sectional dimension of the cooling chamber or region 1820is approximately 1 to 3 times (e.g., 1 to 1.1, 1.1 to 1.2, 1.2 to 1.3,1.3 to 1.4, 1.4 to 1.5, 1.5 to 1.6, 1.6 to 1.7, 1.7 to 1.8, 1.8 to 1.9,1.9 to 2.0, 2.0 to 2.1, 2.1 to 2.2, 2.2 to 2.3, 2.3 to 2.4, 2.4 to 2.5,2.5 to 2.6, 2.6 to 2.7, 2.7 to 2.8, 2.8 to 2.9, 2.9 to 3, values betweenthe foregoing, etc.) the diameter or cross-section dimension of thefluid conduit or passage 1804, as desired or required. In otherembodiments, the diameter or other cross-sectional dimension of thecooling chamber or region 1820 is approximately greater than 3 times thediameter or cross-section dimension of the fluid conduit or passage1804, as desired or required (e.g., 3 to 3.5, 3.5 to 4, 4 to 5, valuesbetween the foregoing, greater than 5, etc.). In other embodiments, thediameter or cross-section dimension of the cooling chamber or region1820 is similar or identical to that of the fluid conduit or passage1804 (or smaller than that of the fluid conduit or passage), as desiredor required.

FIG. 14 illustrates a distal end of a catheter or other medicalinstrument of another embodiment of an ablation system 1900. As shown,the catheter comprises one or more energy delivery members 1930 (e.g., asplit-tip RF electrode, another type of electrode, another type ofablation member, etc.) along its distal end. Like in FIG. 13, thedepicted arrangement comprises an active cooling system using one ormore fluid conduits or passages that extend at least partially throughthe interior of the catheter or other medical instrument.

With continued reference to FIG. 14, the catheter or medical instrumentof the ablation system 1900 includes a closed irrigation system (e.g.,non-open irrigation system) in which cooling fluid (e.g., saline) iscirculated at least partially through an interior of the catheter (e.g.,to and/or near the location of the electrode or other energy deliverymember) to transfer heat away from such electrode or other energydelivery member. As shown, the system can include two separate conduitsor passages 1904, 1906 extending at least partially through the interiorof the catheter or other medical instrument configured for placementwithin and/or adjacent targeted tissue of a subject. In someembodiments, one fluid conduit or passage 1904 is configured to deliverfluid (e.g., saline) to the distal end of the catheter or instrument(e.g., adjacent the electrode, ablation member or other energy deliverymember), while a separate conduit or passage 1906 is configured toreturn the cooling fluid delivered to or near the distal end of thecatheter or other medical instrument proximally. In other embodiments,more than one passage or conduit delivers fluid to the distal end and/ormore than one passage or fluid returns fluid from the distal end, asdesired or required.

In the embodiment of FIG. 14, the fluid delivery conduit or passage 1904is in fluid communication with a cooling chamber or region 1920 thatextends within an interior of the electrode or other energy deliverymember 1930. In the depicted arrangement, the outlet 1905 of the fluiddelivery conduit or passage 1904 is located at a location proximal tothe distal end or inlet 1907 of the fluid return conduit or passage1906. Thus, in the illustrated embodiment, the cooling chamber or region1920 generally extends between the outlet 1905 of the fluid deliveryconduit or passage 1904 and the inlet 1907 of the fluid return conduitor passage 1906. However, in other embodiments, the length, orientation,location and/or other details of the cooling chamber or portion 1920 canvary, as desired or required. Further, in some embodiments, a catheteror other medical instrument can include a closed fluid cooling system(e.g., wherein cooling fluid is circulated through the catheter ormedical instrument) without the inclusion of a separate cooling chamberor portion. Regardless of the exact orientation of the various fluiddelivery and/or return lines (e.g., passages, conduits, etc.) of thecatheter or medical instrument in a closed-loop fluid cooling system,fluid is simply circulated through at least a portion of the catheter orother medical instrument (e.g., adjacent and/or in the vicinity of theelectrode or energy delivery member being energized) to selectively andadvantageously transfer heat away from the electrode or energy deliverymember. Thus, in such embodiments, the various fluid conduits orpassages are in thermal communication with the electrode or other energydelivery member.

In some embodiments, it is advantageous to transfer heat away from theelectrode (or other energy delivery member) of an ablation system, andthus, the targeted tissue of the subject, without expelling ordischarging cooling fluid (e.g., saline) into the subject. For example,in some arrangements, discharging saline or other cooling fluid into theheart, blood vessel and/or other targeted region of the subject canbring about negative physiological consequences to the subject (e.g.,heart failure). Thus, in some embodiments, it is preferred to treat asubject with an ablation system that includes a catheter or othermedical instrument with a closed fluid cooling system or without anactive fluid cooling system altogether.

As with the embodiment of FIG. 14 (and/or other embodiments disclosedherein), the depicted catheter includes one or more heat shunt members1950 that are in thermal communication with the electrode, ablationmember or other energy delivery member 1930 of the system 1900. Asdiscussed above, the heat shunt members 1950 can include industrialdiamond, Graphene, silica, other carbon-based materials with favorablethermal diffusivity properties and/or the like. In some embodiments, thethermal diffusivity of the material(s) included in the heat shuntmembers and/or of the overall heat shunt network or assembly (e.g., whenviewed as a unitary member or structure) is greater than 1.5 cm²/sec(e.g., 1.5-2, 2-2.5, 2.5-3, 3-4, 4-5, 5-6, 6-7, 7-8, 8-9, 9-10, 10-11,11-12, 12-13, 13-14, 14-15, 15-20 cm²/sec, values between the foregoingranges, greater than 20 cm²/sec).

FIG. 15 illustrates yet another embodiment of a catheter or othermedical instrument of an ablation system 2000 can includes one or moreheat transfer members 2050 (e.g., heat shunt members) along and/or nearits distal end. Unlike the arrangements of FIGS. 13 and 14 discussedherein, the depicted embodiment does not include an active fluid coolingsystem. In other words, the catheter or other medical instrument doesnot comprise any fluid conduits or passages. Instead, in someembodiments, as illustrated in FIG. 15, the distal end of the cathetercomprises one or more interior members (e.g., interior structuralmembers) 2070 along its interior. Such interior members 2070 can includea member or material having favorable thermal diffusivitycharacteristics. In some embodiments, the interior member 2070 comprisesidentical or similar thermal diffusivity characteristics or propertiesas the heat shunt members 2050, such as, for example, industrial diamondor Graphene. In some embodiments, the thermal diffusivity of thematerial(s) included in the interior member 2070 and/or of the overallheat shunt network or assembly (e.g., when viewed as a unitary member orstructure) is greater than 1.5 cm²/sec (e.g., 1.5-2, 2-2.5, 2.5-3, 3-4,4-5, 5-6, 6-7, 7-8, 8-9, 9-10, 10-11, 11-12, 12-13, 13-14, 14-15, 15-20cm²/sec, values between the foregoing ranges, greater than 20 cm²/sec).However, in other embodiments, the interior member(s) do not includehigh heat shunting materials and/or members. In other embodiments,however, the interior member 2070 does not include materials or memberssimilar to those as the heat shunt members 2050. For example, in somearrangements, the interior member(s) 2070 can include one or morecomponents or members that comprise material(s) having a thermaldiffusivity less than 1 cm²/sec.

With continued reference to the embodiment of FIG. 15, the volume alongthe distal end of the catheter or medical instrument includes astructural member that at least partially occupies said volume. This isin contrast to other embodiments disclosed herein, wherein at least aportion of the distal end of the catheter or medical instrument includesa cavity (e.g., a cooling chamber) that is configured to receive coolingfluid (e.g., saline) when such cooling fluid is delivered and/orcirculated through the catheter or medical instrument.

In embodiments such as the one illustrated in FIG. 15, wherein no activefluid cooling is incorporated into the design of the catheter or othermedical instrument of the ablation system 2000, heat generated by and/orat the electrode (or other energy delivery member) 2030 can be moreevenly dissipated along the distal end of the catheter or medicalinstrument as a result of the heat dissipation properties of the heattransfer members 2050, including, without limitation, heat shuntmembers, (and/or the interior member 2070, to the extent that theinterior member 2070 also comprises favorable heat shunting properties,e.g., materials having favorable thermal diffusivity characteristics).Thus, the heat shunt members 2050 can help dissipate heat away from theelectrode or other energy delivery member (e.g., either via direct orindirect thermal contact with the electrode or other energy deliverymember) to reduce the likelihood of any localized hotspots (e.g., alongthe distal and/or proximal ends of the electrode or other energydelivery member). Accordingly, heat can be more evenly distributed withthe assistance of the heat shunt member 2050 along a greater volume,area and/or portion of the catheter. As discussed above, the use of heatshunting members can quickly and efficiently transfer heat away from theelectrode and the tissue being treated during use. The use of materialsthat comprises favorable thermal diffusivity properties can accomplishthe relatively rapid heat transfer without the negative effect of heatretention (e.g., which may otherwise cause charring, thrombus formationand/or other heat-related problems).

Further, in some embodiments, the flow of blood or other natural bodilyfluids of the subject in which the catheter or medical instrument ispositioned can facilitate with the removal of heat away from theelectrode or other energy delivery member. For example, the continuousflow of blood adjacent the exterior of the catheter during use can helpwith the removal of heat away from the distal end of the catheter. Suchheat transfer can be further enhanced or otherwise improved by thepresence of one or more heat shunt members that are in thermalcommunication with the exterior of the catheter. For example, in somearrangements, such as shown in FIG. 15, one or more heat shunt members2050 can extend to the exterior of the catheter or other medicalinstrument. Thus, as blood (and/or other bodily fluids) moves past thecatheter or other medical instrument when the catheter or medicalinstrument is inserted within the subject during use, heat can beadvantageously transferred through the heat shunt members 2050 to theblood and/or other bodily fluids moving adjacent the catheter. Again,the use of heat shunt materials with favorable thermal diffusivitycharacteristics will ensure that heat is not retained within suchmaterials, thereby creating a safer ablation system and treatmentprocedure.

FIGS. 16A and 16B illustrate another embodiment of a catheter or othermedical instrument of an ablation system 2100 that includes one or moreheat transfer members 2050 (e.g., heat shunt members) along and/or nearits distal end. Unlike other embodiments disclosed herein, theillustrated system includes a proximal electrode or electrode portion2130 that extends deeper into the interior of the catheter. For example,as depicted in the side cross-sectional view of FIG. 16B, the proximalelectrode 2130 can extend to or near the outside of the irrigationchannel 2120. As discussed herein, the irrigation channel 2120 cancomprise one or more metals, alloys and/or other rigid and/or semi-rigidmaterials, such as, for example, stainless steel.

With continued reference to FIGS. 16A and 16B, the proximal electrode orproximal electrode portion 2130 can be part of a split-tip electrodesystem, in accordance with the various split-tip embodiments disclosedherein. Thus, in some embodiments, in order for the split tip electrodeconfiguration to operate properly, the distal electrode 2110 iselectrically isolated from the proximal electrode 2130. In theillustrated configuration, since the proximal electrode 2130 extends toor near the metallic (and thus, electrically conductive) irrigation tube2120, at least one electrically insulative layer, coating, member,portion, barrier and/or the like 2128 can be advantageously positionedbetween the electrode 2130 and the irrigation tube 2120. In someembodiments, for example, the electrically insulative member 2128comprises one or more layers of polyimide, other polymeric materialand/or another electrically insulative material, as desired or required.Such an electrically-insulative layer and/or other member 2128 can takethe place of diamond and/or another electrically-insulative heatshunting member that may otherwise be positioned around the irrigationtube 2120 to electrically isolate the distal electrode 2110 from theproximal electrode 2130.

According to any of the embodiments disclosed herein, the proximaland/or the distal electrodes 2130, 2110 can comprise one or more metalsand/or alloys. For example, the electrodes can include platinum,stainless steel and/or any other biocompatible metal and/or alloy. Thus,in some embodiments, the thicker proximal electrode 2130 that extends toor near the irrigation tube 2120 can be referred to as a “slug,” e.g.,“a platinum slug.” As discussed, in such arrangements, the need for aninternal diamond and/or other heat shunting member can be eliminated.Instead, in such embodiments, as depicted in FIG. 16B, the proximal anddistal ends of the “slug” or thicker proximal electrode 2130 can beplaced in thermal communication with one or more heat shunting members(e.g., diamond) to help shunt heat away from the electrode 2130 and/orthe tissue of the subject being treated. Thus, in some embodiments, theproximal and/or the distal faces of the proximal electrode or slug 2130can be placed in good thermal contact with adjacent heat shuntingmembers, as desired or required.

With continued reference to FIG. 16B, according to some embodiments, atleast a portion 2222 of the irrigation tube 2120 is perforated and/orhas one or more openings 2123. In some embodiments, such openings 2123can place an irrigation fluid carried within the interior of theirrigation channel 2120 in direct physical and thermal communicationwith an adjacent heat shunting member (e.g., diamond, Graphene, silica,etc.) to quickly and efficiently transfer heat away from the electrodeand/or tissue being treated. In some embodiments, the direct physicaland/or thermal communication between the irrigation fluid and theshunting member helps provide improved heat transfer to the irrigationfluid (e.g., saline) passing through the interior of the irrigationchannel 2120. In the illustrated embodiment, the openings 2123 along theperforated portion 2222 are generally circular in shape and evenlydistributed relative to each other (e.g., comprise a generally evendistribution or spacing relative to each other). However, in otherarrangements, the size, shape, spacing and/or other characteristics ofthe openings 2123 along the perforated or direct contact region 2122 ofthe channel 2120 can vary, as desired or required. For example, in someembodiments, the openings 2123 can be oval, polygonal (e.g., square orrectangular, triangular, pentagonal, hexagonal, octagonal, etc.),irregular and/or the like. In some embodiments, the openings are slottedor elongated.

Regardless of their exact shape, size, orientation, spacing and/or otherdetails, the openings 2123 that comprise the perforated or directcontact region 2122 of the channel 2120 can provide direct contactbetween the irrigation fluid and the adjacent diamond (and/or anotherheat shunting member) 1150 for 30% to 70% (e.g., 30-35, 35-40, 40-45,45-50, 50-55, 55-60, 60-65, 65-70%, percentages between the foregoingranges, etc.) of the surface area of the perforated or direct contactregion 2122 of the channel 2120. In other embodiments, the openings 2123that comprise the perforated or direct contact region 2122 of thechannel 2120 can provide direct contact between the irrigation fluid andthe adjacent diamond (and/or another heat shunting member) 2150 for lessthan 30% (e.g., 1-5, 5-10, 10-15, 15-20, 20-25, 25-30%, percentagesbetween the foregoing ranges, less than 1%, etc.) or greater than 70%(e.g., 70-75, 75-80, 80-85, 85-90, 90-95, 95-99%, percentages betweenthe foregoing ranges, greater than 99%, etc.) of the surface area of theperforated or direct contact region 2122 of the channel 2120, as desiredor required. Such a perforated or direct contact region 2122 can beincorporated into any of the embodiments disclosed herein. In addition,any of the embodiments disclosed herein, including, without limitation,the system of FIGS. 16A and 16B, can include more than one perforated ordirect contact region 2122. For example, the embodiment of FIGS. 16A and16B can include a second perforated or direct contact region along thedistal end of the proximal slug or electrode 2130 and/or along any otherportion adjacent a heat shunting member.

As illustrated in FIG. 16B, the distal end of an irrigation tube (e.g.,a flexible polyurethane or other polymeric conduit) 2104 that is influid communication with the irrigation channel 2120 that extendsthrough the distal end of the catheter or other medical instrument canbe positioned at least partially within an interior of such a channel2120. Such a configuration can be incorporated into any of theembodiments disclosed herein or variations thereof. In some embodiments,the distal portion of the irrigation tube 2104 can be sized, shapedand/or otherwise configured to press-fit within an interior of thedistal channel 2120. However, in some embodiments, one or more otherattachment devices or methods, such as, for example, adhesives, heatbonding, fasteners, etc., can be used to help secure the irrigation tube2104 to the irrigation channel 2120, as desired or required.

Another embodiment of a distal end of a catheter or other medicalinstrument 2200 comprising heat shunting characteristics is illustratedin FIG. 16C. As shown, the proximal electrode or slug 2230 extendstoward the interior of the catheter (e.g., to or near the irrigationchannel 2220). However, the depicted electrode 2230 is generally thinnerthan (e.g., does not extend as far as) the embodiment of FIGS. 16A and16B. In the illustrated embodiment, one or more heating shunting members(e.g., diamond, Graphene, silica, etc.) with favorable thermaldiffusivity characteristics are positioned between the interior of theproximal electrode or slug 2230 and the irrigation channel 2220. Thus,is such an arrangement, not only can heat generated at or along theelectrode 2230 and/or the tissue of the subject being treated be morequickly and efficiently transferred away from the electrode and/ortissue, but the diamond or other electrically-insulating heat shuntingmember or network 2250 provides the necessary electrical insulationbetween the metallic (e.g., stainless steel) irrigation channel 2220 andthe proximal electrode or slug 2230. As noted herein, such electricalisolation is helpful with a split-tip design.

A distal portion 2300 of another embodiment of an ablation system isillustrated in FIGS. 17A and 17B. As shown, the system comprises asplit-tip design, with a proximal electrode or slug 2330 and a distalelectrode 2310. Further, the catheter or other medical instrumentincludes one or more heat transfer members 2350, including, withoutlimitation, a heat shunt network (e.g., comprising diamond, Graphene,silica and/or other materials with favorable thermal diffusivityproperties). According to some embodiments, as depicted in theillustrated arrangement, the heat shunt network 2350 can include ringsthat extend to the exterior of the catheter or instrument and/or one ormore interior members that are positioned within (e.g., underneath) theproximal electrode 2330, as desired or required. In addition, as withother embodiments disclosed herein, one or more temperature sensors2392, 2394 can be provide along one or more portions of the system(e.g., along or near the distal electrode 2310, along or near theproximal heat shunt member, along or near the proximal electrode 2330,etc.) to help detect the temperature of tissue being treated. Asdiscussed in greater detail in such temperature sensors (e.g.,thermocouples) can also be used to detect the orientation of the tip, todetermine whether (and/or to what extent) contact is being made betweenthe tip and tissue and/or the like.

With continued reference to the embodiment of FIGS. 17A and 17B, thecatheter or other medical instrument can include a proximal coupling ormember 2340. As shown, such a coupling or member 2340 is configured toconnect to and be placed in fluid communication with an irrigationconduit (e.g., polyurethane, other polymeric or other flexible conduit,etc.) 2304. For example, in the illustrated embodiment, the distal endof the irrigation conduit 2304 is sized, shaped and otherwise configuredto be inserted within a proximal end (e.g., recess) of the coupling2340. In some embodiments, the irrigation conduit 2304 is press-fitwithin the recess of the coupling 2340. In other arrangements, however,one or more other attachment devices or methods can be used to securethe conduit 2304 to the coupling 2340 (e.g., adhesive, weld, fasteners,etc.), either in lieu or in addition to a press-fit connection, asdesired or required. Regardless of the exact mechanism of securementbetween the irrigation conduit 2304 and the coupling 2340, fluid passingthrough the conduit 2304 can enter into a manifold 2342 of the coupling2340. In some embodiments, the manifold 2342 can divide the irrigationfluid flow into two or more pathways 2344. However, in some embodiments,the coupling 2340 does not have a manifold. For example, irrigationfluid entering the coupling 2340 can be routed only along a single fluidpathway, as desired or required.

In the embodiment of FIGS. 17A and 17B, the manifold (or other flowdividing feature, device or component) 2342 of the coupling 2340separates the irrigation flow into three different fluid pathways. Asshown, each such fluid pathway can be placed in fluid communication witha separate fluid conduit or sub-conduit 2320. In some embodiments, suchfluid conduits 2320 are equally spaced apart (e.g., radially) relativeto the centerline of the catheter or other medical instrument. Forexample, the conduits 2320 can be spaced apart at or approximately at120 degrees relative to each other. As shown, the conduits 2320 extend,at least partially, through the proximal heat shunt member 2350 and theproximal slug or electrode 2330. However, in other embodiments, theorientation, spacing and/or other details of the manifold 2342, 2344and/or the fluid conduits 2320 can vary. In addition, the number offluid conduits 2320 originating from the manifold system can be greaterthan 3 (e.g., 4, 5, 6, 7, greater than 7, etc.) or less than 3 (e.g., 1,2), as desired or required.

In some embodiments in which the system comprises an open-irrigationsystem, as illustrated in the longitudinal cross-sectional view of FIG.17B, one or more irrigation fluid outlets 2332 a, 2332 b, 2332 c can beprovided along one or more of the fluid conduits 2320. As shown, suchfluid outlets 2332 can provided within the proximal electrode 2330.However, in other embodiments, such outlets 2332 can be included withinone or more other portions of the system (e.g., a heat shunt member2350, the distal electrode 2310, etc.), either in lieu of or in additionto the proximal electrode 2330. Such a configuration (e.g., oneincluding a manifold and/or openings through the proximal electrode) canbe incorporated into any of the ablation system embodiments disclosedherein. As with other irrigation system arrangements disclosed herein,heat can be shunted (e.g., from the electrode, the tissue being treated,one or more other portions of the system, etc.) to the irrigation fluidpassing through the conduits and/or fluid outlets to help quickly andefficiently dissipate (e.g., shunt) heat from the system during use. Insome embodiments, as illustrated in FIGS. 17A and 17B, the relativesize, shape and/or other configuration of two or more of the fluidoutlets 2332 can vary. For example, in some arrangements, in order tobetter balance the fluid hydraulics of fluid passing through eachconduit 2320 (e.g., to better balance the flow rate passing through eachoutlet 2332), the proximal fluid outlets can be smaller than one or moreof the distal fluid outlets. However, in other embodiments, two or more(e.g., most or all) of the fluid outlets 2332 include the identicalshape, size and/or other properties.

In some embodiments, the orientation of the fluid outlets can be skewedrelative to the radial direction of the catheter or other medicalinstrument in which they are located. Such a skewing or offset can occurfor any fluid outlets located along the distal end of the catheter orother medical instrument (e.g., fluid outlets located along the distalelectrode as shown in FIGS. 13, 16A and 16B and 16C, fluid outletslocated along the proximal electrode as shown in FIGS. 17A and 17B,etc.). The extent to which the outlets are skewed or offset (e.g.,relative to the radial direction of the catheter or medical instrument,relative to a direction perpendicular to the longitudinal centerline ofthe catheter or medical instrument) can vary, as desired or required. Byway of example, the fluid openings can be skewed or offset relative tothe radial direction by 0 to 60 degrees (e.g., 0-5, 5-10, 10-15, 15-20,20-25, 25-30, 30-35, 35-40, 40-45, 45-50, 50-55, 55-60 degrees, anglesbetween the foregoing ranges, etc.). In some embodiments, the fluidopenings are skewed or offset relative to the radial direction by morethan 60 degrees (e.g., 60-65, 65-70, 70-75 degrees, angles between theforegoing ranges, greater than 70 degrees, etc.), as desired orrequired.

According to some embodiments, fluid outlets or openings located alongor near the distal electrode are skewed or offset distally (e.g., in adirection distal to the location of the corresponding fluid outlet oropening). In some embodiments, fluid outlets or openings located alongor near the proximal electrode are skewed or offset proximally (e.g., ina direction proximal to the location of the corresponding fluid outletor opening). Thus, in some embodiments, irrigation fluid exiting at ornear the distal electrodes is delivered in a direction distal to thecorresponding fluid outlet(s), and irrigation fluid exiting at or nearthe proximal electrodes is delivered in a direction proximal to thecorresponding fluid outlet(s). In some embodiments, such a configurationcan assist with cooling hot spots that may otherwise be created along ornear the electrode. Such a configuration could also help dilute theblood in those areas to help reduce the chance of thrombus and/orcoagulation formation.

Multiple Temperature Sensors

According to some embodiments, a medical instrument (for example,ablation catheter) can include multiple temperature-measurement devices(for example, thermocouples, thermistors, other temperature sensors)spaced axially at different locations along a distal portion of themedical instrument. The axial spacing advantageously facilitatesmeasurement of a meaningful spatial temperature gradient. Each of thetemperature-measurement devices may be isolated from each of the othertemperature-measurement devices to provide independent temperaturemeasurements. The temperature-measurement devices may be thermallyinsulated from one or more energy delivery members (for example,radiofrequency electrodes) so as not to directly measure the temperatureof the energy delivery member(s), thereby facilitating temperaturemeasurements that are isolated from the thermal effects of the energydelivery member(s). The medical instrument may comprise a firstplurality (for example, set, array, group) of temperature sensorspositioned at or adjacent a distal tip, or terminus, of the medicalinstrument. The first plurality of temperature sensors may be spacedapart (for example, circumferentially, radially) around the medicalinstrument along a first cross-sectional plane of the medicalinstrument, in an equidistant manner or non-equidistant manner. Themedical instrument may also comprise a second plurality of temperaturesensors spaced proximally from the first plurality of temperaturesensors along a second cross-sectional plane of the medical instrumentthat is proximal of the first cross-sectional plane, thereby allowingfor temperature measurements to be obtained at multiple locations. Insome embodiments, the second plurality of temperature sensors ispositioned adjacent to a proximal end (for example, edge) of theelectrode or other energy delivery member (if the medical instrument(for example, ablation catheter) comprises a single electrode or otherenergy delivery member) or of the proximal-most electrode or otherenergy delivery member (if the medical instrument comprises multipleelectrode members or other energy delivery members).

The temperature measurements obtained from the temperature sensors mayadvantageously be used to determine, among other things, an orientationof the distal tip of the medical instrument with respect to a tissuesurface, to determine an estimated temperature of a peak temperaturezone of a lesion formed by the medical instrument (for example, ablationcatheter), and/or an estimated location of the peak temperature zone ofthe lesion. In some embodiments, the determinations made using thetemperature sensors or other temperature-measurement devices can be usedto adjust treatment parameters (for example, target temperature, power,duration, orientation) so as to prevent char or thrombus if used in ablood vessel and/or to control lesion parameters (for example, depth,width, location of peak temperature zone, peak temperature), thusproviding more reliable and safer treatment (for example, ablation)procedures. Accordingly, upon implementation of a control scheme thatregulates the delivery of power or other parameters to an energydelivery member (for example, RF electrode, microwave emitter,ultrasound transducer, cryogenic emitter, other emitter, etc.) locatedalong the distal end of a medical apparatus (for example, catheter,probe, etc.), the target level of treatment can be accomplished withoutnegatively impacting (for example, overheating, over-treating, etc.) thesubject's tissue (for example, within and/or adjacent a treatmentvolume).

The term peak temperature, as used herein, can include either a peak orhigh temperature (for example, a positive peak temperature) or a troughor low temperature (for example, negative peak temperature). As aresult, determination of the peak temperature (for example, maximum orminimum temperature or other extreme temperature) within targeted tissuecan result in a safer, more efficient and more efficacious treatmentprocedure. In some embodiments, when, for example, cryoablation isperformed, the systems, devices and/or methods disclosed herein can beused to determine the trough or lowest temperature point, within thetreatment (for example, ablation) volume. In some embodiments,technologies that cool tissue face similar clinical challenges ofcontrolling the tissue temperature within an efficacious and safetemperature range. Consequently, the various embodiments disclosedherein can be used with technologies that either cool or heat targetedtissue.

Several embodiments of the invention are particularly advantageousbecause they include one, several or all of the following benefits: (i)reduction in proximal edge heating, (ii) reduced likelihood of char orthrombus formation, (iii) providing feedback that may be used to adjustablation procedures in real time, (iv) provides noninvasive temperaturemeasurements, (v) does not require use of radiometry; (vi) providessafer and more reliable ablation procedures; and (vii) tissuetemperature monitoring and feedback during irrigated or non-irrigatedablation.

For any of the embodiments disclosed herein, a catheter or otherminimally-invasive medical instrument can be delivered to the targetanatomical location of a subject (for example, atrium, pulmonary veins,other cardiac location, renal artery, other vessel or lumen, etc.) usingone or more imaging technologies. Accordingly, any of the ablationsystems disclosed herein can be configured to be used with (for example,separately from or at least partially integrated with) an imaging deviceor system, such as, for example, fluoroscopy technologies, intracardiacechocardiography (“ICE”) technologies and/or the like. In someembodiments, energy delivery is substituted with fluid delivery (forexample, hot fluid, cryogenic fluid, chemical agents) to accomplishtreatment.

FIG. 18A illustrates a perspective view of a distal portion of anopen-irrigated ablation catheter 3120A comprising multipletemperature-measurement devices 3125, according to one embodiment. Asshown, the embodiment of the ablation catheter 3120A of FIG. 18A is anopen-irrigated catheter comprising a split-tip electrode design. Thesplit-tip electrode design comprises a dome- or hemispherical-shapeddistal tip electrode member 3130, an insulation gap 3131 and a proximalelectrode member 3135. The ablation catheter 3120A comprises multipleirrigation ports 3140 and a thermal transfer member 3145.

The temperature-measurement devices 3125 comprise a first (for example,distal) group of temperature-measurement devices 3125A positioned inrecesses or apertures formed in the distal electrode member 3130 and asecond (for example, proximal) group of temperature-measurement devices3125B positioned in slots, notches or openings formed in the thermaltransfer member 3145 proximate or adjacent the proximal edge of theproximal electrode member 3135. The temperature-measurement devices 3125may comprise thermocouples, thermistors, fluoroptic sensors, resistivetemperature sensors and/or other temperature sensors. In variousembodiments, the thermocouples comprise nickel alloy, platinum/rhodiumalloy, tungsten/rhenium alloy, gold/iron alloy, noble metal alloy,platinum/molybdenum alloy, iridium/rhodium alloy, pure noble metal, TypeK, Type T, Type E, Type J, Type M, Type N, Type B, Type R, Type S, TypeC, Type D, Type G, and/or Type P thermocouples. A reference thermocouplemay be positioned at any location along the catheter 120A (for example,in a handle or within a shaft or elongate member of the catheter 3120A.In one embodiment, the reference thermocouple is thermally insulatedand/or electrically isolated from the electrode member(s). The electrodemember(s) may be substituted with other energy delivery members.

In some embodiments, the temperature-measurement devices are thermallyinsulated from the electrode members 3130, 3135 so as to isolate thetemperature measurements from the thermal effects of the electrodemembers (for example, to facilitate measurement of surroundingtemperature, such as tissue temperature, instead of measuringtemperature of the electrode members). As shown, thetemperature-measurement devices 3125 may protrude or extend outward froman outer surface of the ablation catheter 3120A. In some embodiments,the temperature-measurement devices 3125 may protrude up to about 1 mmaway from the outer surface (for example, from about 0.1 mm to about 0.5mm, from about 0.5 mm to about 1 mm, from about 0.6 mm to about 0.8 mm,from about 0.75 mm to about 1 mm, or overlapping ranges thereof). Thedome shape of the distal tip electrode member 3130 and/or the outwardprotrusion or extension of the temperature-measurement devices 3125 mayadvantageously allow the temperature-measurement devices to be burieddeeper into tissue and away from effects of the open irrigation providedby irrigation ports 3140, in accordance with several embodiments. Theproximal group of temperature-measurement devices and the distal groupof temperature-measurement devices may protrude the same amount ordifferent amounts (as a group and/or individually within each group). Inother embodiments, the temperature-measurement devices 3125 are flush orembedded within the outer surface (for example, 0.0 mm, −0.1 mm, −0.2mm, −0.3 mm, −0.4 mm, −0.5 mm from the outer surface).

With reference to FIG. 18D, a portion of the ablation catheter 3120Cwhere the temperature-measurement devices 3125 are positioned may have alarger outer diameter or other outer cross-sectional dimension thanadjacent portions of the ablation catheter 3120C so as to facilitatedeeper burying of the temperature-measurement devices within tissue andto further isolate the temperature measurements from the thermal effectsof the electrode members or fluid (for example, saline or blood). Asshown in FIG. 18D, the portion of the ablation catheter 3120C comprisingthe proximal group of temperature-measurement devices 3125B comprises abulge, ring or ridge 3155 having a larger outer diameter than adjacentportions.

In some embodiments, the temperature-measurement devices 3125 areadapted to be advanced outward and retracted inward. For example, thetemperature-measurement devices 3125 may be in a retracted position(within the outer surface or slightly protruding outward) duringinsertion of the ablation catheter and movement to the treatmentlocation to reduce the outer profile and facilitate insertion to thetreatment location and may be advanced outward when at the treatmentlocation. The features described above in connection with ablationcatheter 3120C of FIG. 18D may be employed with any of the otherablation catheters described herein.

Returning to FIG. 18A, the proximal and distal groups oftemperature-measurement devices 3125 may each comprise two, three, four,five, six, or more than six temperature-measurement devices. In theillustrated embodiment, the proximal and distal groups oftemperature-measurement devices 3125 each consist of threetemperature-measurement devices, which may provide a balance betweenvolumetric coverage and reduced number of components, according to oneembodiment. The number of temperature-measurement devices may beselected to balance accuracy, complexity, volumetric coverage, variationin tip to tissue apposition, cost, number of components, and/or sizeconstraints. As shown in FIG. 18A, the temperature-measurement devicesmay be equally spaced apart around a circumference of the ablationcatheter 3120A or spaced an equal number of degrees apart from eachother about a central longitudinal axis extending from a proximal end toa distal end of the ablation catheter. For example, when threetemperature-measurement devices are used, they may be spaced about 120degrees apart and when four temperature-measurement devices are used,they may be spaced about 90 degrees apart. In other embodiments, thetemperature-measurement devices 3125 are not spaced apart equally.

As shown in the embodiment of FIG. 18A, the temperature-measurementdevices 3125 of each group may be positioned along the samecross-sectional plane of the ablation catheter 3120A. For example, thedistal temperature-measurement devices 3125A may be positioned to extendthe same distance outward from the dome-shaped surface and the proximaltemperature-measurement devices 3125B may each be spaced the samedistance from the distal tip of the ablation catheter 3120A. As shown inthe embodiment of FIG. 18A, the distal temperature-measurement devices3125A extend in axial direction that is parallel or substantiallyparallel with a central longitudinal axis of the distal portion of theablation catheter 3120A and the proximal temperature-measurement devices3125B extend radially outward from the outer surface of the ablationcatheter 3120A. In other embodiments, the distal temperature-measurementdevices 3125A may not be positioned on the distal surface of the distalterminus but may be positioned on a lateral surface to extend radiallyoutward (similar to the illustrated proximal temperature-measurementdevices 3125B).

As shown in the embodiment of FIG. 18A, the distaltemperature-measurement devices 3125A may be positioned distal of theinsulation gap 3131 and/or of the irrigation ports 3140 and the proximaltemperature-measurement devices 3125B may be positioned proximal to thedistal edge of the proximal electrode member 3135 within the thermaltransfer member 3145. In other embodiments (for example, as shown inFIGS. 22A and 22B), the proximal temperature-measurement devices 3125Bmay be positioned distal to the distal edge of the proximal electrodemember 3135 (for example, within recesses or apertures formed within theproximal electrode member 3135 similar to the recesses or aperturesformed in the distal tip electrode member illustrated in FIG. 18A). Inother embodiments, the distal temperature-measurement devices 3125Aand/or the proximal temperature-measurement devices 3125B may bepositioned at other locations along the length of the ablation catheter3120A. In some embodiments, each distal temperature-measurement device3125A is axially aligned with one of the proximaltemperature-measurement devices 3125B and the spacing between the distaltemperature-measurement devices 3125A and the proximaltemperature-measurement devices is uniform or substantially uniform.

The irrigation ports 3140 may be spaced apart (equidistant or otherwise)around a circumference of the shaft of the ablation catheter 3120A. Theirrigation ports 3140 are in communication with a fluid source, such asa fluid source provided by the irrigation fluid system 70 of FIG. 1. Theirrigation ports facilitate open irrigation and provide cooling to theelectrode members 3130, 3135 and any blood surrounding the electrodemembers 3130, 3135. In some embodiments, the ablation catheter 3120Acomprises three, four, five, six, seven, eight or more than eight exitports 3140. In various embodiments, the exit ports 3140 are spacedbetween 0.005 and 0.015 inches from the proximal edge of the distalelectrode member 3130 so as to provide improved cooling of the thermaltransfer member 3145 at the tissue interface; however, other spacing canbe used as desired and/or required. In other embodiments, the exit ports3140 are spaced apart linearly and/or circumferentially along theproximal electrode member 3135 (as shown, for example, in FIG. 18E).

FIGS. 18B and 18C illustrate a perspective view and a cross-sectionalview, respectively, of a distal portion of an open-irrigated ablationcatheter 3120B having multiple temperature-measurement devices,according to another embodiment. The ablation catheter 3120B may includeall of the structural components, elements and features of the ablationcatheter 3120A described above and ablation catheter 3120A may includeall of the structural components, elements and features described inconnection with FIGS. 18B and 18C. The ablation catheter 3120B comprisesa flat tip electrode member 3130 instead of a dome-shaped tip electrodemember as shown in FIG. 18A.

As best shown in FIG. 18C, the thermal transfer member 3145 is inthermal contact with one or both of the electrode members 3130, 3135.The thermal transfer member 3145 can extend to, near or beyond theproximal end of the proximal electrode member 3135. In some embodiments,the thermal transfer member 3145 terminates at or near the proximal endof the proximal electrode member 3135. However, in other arrangements(as shown in FIG. 18C), the thermal transfer member 3145 extends beyondthe proximal end of the proximal electrode member 3135. In yet otherembodiments, the thermal transfer member 3145 terminates distal of theproximal end (for example, edge) of the proximal electrode member 3135.The thermal transfer member 3145 may extend from the proximal surface ofthe tip electrode member 3130 to location beyond the proximal end of theproximal electrode member 3135. Embodiments wherein the thermal transfermember 3145 extends beyond the proximal end of the proximal electrodemember 3135 may provide increased shunting of proximal edge heatingeffects caused by the increased amount of current concentration at theproximal edge by reducing the heat at the proximal edge throughconductive cooling. In some embodiments, at least a portion of thethermal transfer member 3145 is in direct contact with the tissue (forexample, within insulation gap 3131) and can remove or dissipate heatdirectly from the targeted tissue being heated.

The thermal transfer member 3145 can comprise one or more materials thatinclude favorable heat transfer properties. For example, in someembodiments, the thermal conductivity of the material(s) included in thethermal transfer member is greater than 300 W/m/° C. (for example,300-350, 350-400, 400-450, 450-500, 500-600, 600-700 W/m/° C., rangesbetween the foregoing, greater than 700 W/m/° C., etc.).

Possible materials with favorable thermal conductivity propertiesinclude, but are not limited to, copper, brass, beryllium, other metalsand/or alloys, aluminal ceramics, other ceramics, industrial diamondand/or other metallic and/or non-metallic materials.

According to certain embodiments where the heat transfer memberscomprise heat shunting members, the thermal diffusivity of thematerial(s) included in the heat shunt members and/or of the overallheat shunt assembly (for example, when viewed as a unitary member orstructure) is greater than 1.5 cm²/sec (for example, 1.5-2, 2-2.5,2.5-3, 3-4, 4-5, 5-6, 6-7, 7-8, 8-9, 9-0, 10-11, 11-12, 12-13, 13-14,14-15, 15-20 cm²/sec, values between the foregoing ranges, greater than20 cm²/sec). Thermal diffusivity measures the ability of a material toconduct thermal energy relative to its ability to store thermal energy.Thus, even though a material can be efficient as transferring heat (forexample, can have a relatively high thermal conductivity), it may nothave favorable thermal diffusivity properties, because of its heatstorage properties. Heat shunting, unlike heat transferring, requiresthe use of materials that possess high thermal conductance properties(for example, to quickly transfer heat through a mass or volume) and alow heat capacity (for example, to not store heat). Possible materialswith favorable thermal diffusivity, and thus favorable heat shuntingproperties, include, but are not limited to, industrial diamond,graphene, silica alloys, ceramics, other carbon-based materials and/orother metallic and/or non-metallic materials. In various embodiments,the material used for the heat transfer (for example, diamond) providesincreased visibility of the catheter tip using ICE imaging or otherimaging techniques.

The use of materials with favorable thermal diffusivity properties canhelp ensure that heat can be efficiently transferred away from theelectrode and/or the adjacent tissue during a treatment procedure. Incontrast, materials that have favorable thermal conductivity properties,but not favorable thermal diffusivity properties, such as, for example,copper, other metals or alloys, thermally conductive polypropylene orother polymers, etc., will tend to retain heat. As a result, the use ofsuch materials that store heat may cause the temperature along theelectrode and/or the tissue being treated to be maintained at anundesirably elevated level (for example, over 75 degrees C.) especiallyover the course of a relatively long ablation procedure, which mayresult in charring, thrombus formation and/or other heat-relatedproblems.

Industrial diamond and other materials with the requisite thermaldiffusivity properties for use in a thermal shunting network, asdisclosed in the various embodiments herein, comprise favorable thermalconduction characteristics. Such favorable thermal conduction aspectsemanate from a relatively high thermal conductance value and the mannerin which the heat shunt members of a network are arranged with respectto each other within the tip and with respect to the tissue. Forexample, in some embodiments, as radiofrequency energy is emitted fromthe tip and the ohmic heating within the tissue generates heat, theexposed distal most shunt member (for example, located 0.5 mm from thedistal most end of the tip) can actively extract heat from the lesionsite. The thermal energy can advantageously transfer through theshunting network in a relatively rapid manner and dissipate through theshunt residing beneath the radiofrequency electrode surface the heatshunt network, through a proximal shunt member and/or into the ambientsurroundings. Heat that is shunting through an interior shunt member canbe quickly transferred to an irrigation conduit extending through aninterior of the catheter or other medical instrument. In otherembodiments, heat generated by an ablation procedure can be shuntedthrough both proximal and distal shunt members (for example, shuntmembers that are exposed to an exterior of the catheter or other medicalinstrument, such as shown in many of the embodiments herein).

Further, as noted above, the materials with favorable thermaldiffusivity properties for use in a heat shunt network not only have therequisite thermal conductivity properties but also have sufficiently lowheat capacity values. This helps ensure that the thermal energy isdissipated very quickly from the tip to tissue interface as well as thehot spots on the electrode, without heat retention in the heat shuntingnetwork. The thermal conduction constitutes the primary heat dissipationmechanism that ensures quick and efficient cooling of the tissue surfaceand of the radiofrequency electrode surface. Conversely a heat transfer(for example, with relatively high thermal conductivity characteristicsbut also relatively high heat capacity characteristics) will storethermal energy. Over the course of a long ablation procedure, suchstored heat may exceed 75 degrees Celsius. Under such circumstances,thrombus and/or char formation can undesirably occur.

The thermal convection aspects of the various embodiments disclosedherein two-fold. First, an irrigation lumen of the catheter can absorbthermal energy which is transferred to it through the shunt network.Such thermal energy can then be flushed out of the distal end of theelectrode tip via the irrigation ports. In closed irrigation systems,however, such thermal energy can be transferred back to a proximal endof the catheter where it can be removed. Second, the exposed shuntsurfaces along an exterior of the catheter or other medical instrumentcan further assist with the dissipation of heat from the electrodeand/or the tissue being treated. For example, such heat dissipation canbe accomplished via the inherent convective cooling aspects of the bloodflowing over the surfaces of the electrode.

Accordingly, the use of materials in a heat shunting network withfavorable thermal diffusivity properties, such as industrial diamond,can help ensure that heat is quickly and efficiently transferred awayfrom the electrode and treated tissue, while maintaining the heatshunting network cool (for example, due to its low heat capacityproperties). This can create a safer ablation catheter and relatedtreatment method, as potentially dangerous heat will not be introducedinto the procedure via the heat shunting network itself.

In some embodiments, the heat shunt members disclosed herein draw outheat from the tissue being ablated and shunt it into the irrigationchannel. Similarly, heat is drawn away from the potential hot spots thatform at the edges of electrodes and are shunted through the heat shuntnetwork into the irrigation channel. From the irrigation channel, viaconvective cooling, heat can be advantageously released into the bloodstream and dissipated away. In closed irrigation systems, heat can beremoved from the system without expelling irrigation fluid into thesubject.

According to some embodiments, the various heat shunting systemsdisclosed herein rely on heat conduction as the primary coolingmechanism. Therefore, such embodiments do not require a vast majority ofthe heat shunting network to extend to an external surface of thecatheter or other medical instrument (for example, for direct exposureto blood flow). In fact, in some embodiments, the entire shunt networkcan reside within an interior of the catheter tip (i.e., with no portionof the heat shut network extending to an exterior of the catheter orother medical instrument). Further, the various embodiments disclosedherein do not require electrical isolation of the heat shunts from theelectrode member or from the irrigation channel.

As shown in FIG. 18C, the thermal transfer member 3145 is also inthermal contact with a heat exchange chamber (for example, irrigationconduit) 3150 extending along an interior lumen of the ablation catheter3120B. For any of the embodiments disclosed herein, at least a portionof a thermal transfer member (for example, heat shunt member) that is inthermal communication with the heat exchange chamber 3150 extends to anexterior surface of the catheter, adjacent to (and, in some embodiments,in physical and/or thermal contact with) one or more electrodes or otherenergy delivery members. Such a configuration, can further enhance thecooling of the electrode(s) or other energy delivery member(s) when thesystem is activated, especially at or near the proximal end of theelectrode(s) or energy delivery member(s), where heat may otherwise tendto be more concentrated (for example, relative to other portions of theelectrode or other energy delivery member). According to someembodiments, thermal conductive grease and/or any other thermallyconductive material (for example, thermally-conductive liquid or otherfluid, layer, member, coating and/or portion) can be used to place thethermal transfer member 3145 in thermal communication with the heatexchange chamber (for example, irrigation conduit) 3150, as desired orrequired. In such embodiments, such a thermally conductive materialplaces the electrode members 3130, 3135 in thermal communication, atleast partially, with the irrigation conduit 3150.

The irrigation conduit(s) 3150 can be part of an open irrigation system,in which fluid exits through the exit ports or openings 3140 along thedistal end of the catheter (for example, at or near the electrode member3130) to cool the electrode members and/or the adjacent targeted tissue.In various embodiments, the irrigation conduit 3150 comprises one ormore metallic and/or other favorable heat transfer (for example, heatshunting) materials (for example, copper, stainless steel, other metalsor alloys, ceramics, polymeric and/or other materials with relativelyfavorable heat transfer properties, etc.). The irrigation conduit 3150can extend beyond the proximal end of the proximal electrode member 3135and into the proximal portion of the thermal transfer member 3145. Theinner wall of the irrigation conduit 3150 may comprise a biocompatiblematerial (such as stainless steel) that forms a strong weld or bondbetween the irrigation conduit 3150 and the material of the electrodemember(s).

In some embodiments, the ablation catheters 3120 only compriseirrigation exit openings 3140 along a distal end of the catheter (forexample, along a distal end of the distal electrode member 3130). Insome embodiments, the system does not comprise any irrigation openingsalong the thermal transfer member 3145.

The thermal transfer member 3145 may advantageously facilitate thermalconduction away from the electrode members 3130, 3135, thereby furthercooling the electrode members 3130, 3135 and reducing the likelihood ofchar or thrombus formation if the electrode members are in contact withblood. The thermal transfer member 3145 may provide enhanced cooling ofthe electrode members 3130, 3135 by facilitating convective heattransfer in connection with the irrigation conduit 3150 in addition tothermal conduction.

Heat transfer (for example, heat shunting) between the thermal transfermember 3145 and the electrode members 3130, 3135 can be facilitated andotherwise enhanced by eliminating air gaps or other similar spacesbetween the electrode members and the thermal transfer member. Forexample, one or more layers of an electrically conductive material (forexample, platinum, gold, other metals or alloys, etc.) may be positionedbetween the interior of the electrode member and the exterior of thethermal transfer member 3145. Such layer(s) can be continuously orintermittently applied between the electrode member (or another type ofablation member) and the adjacent thermal transfer member. Further, suchlayer(s) can be applied using one or more methods or procedures, suchas, for example, sputtering, other plating techniques and/or the like.Such layer(s) can be used in any of the embodiments disclosed herein orvariations thereof. In addition, the use of a heat shunting networkspecifically can help transfer heat away from the tissue being treatedby the electrode member(s) without itself absorbing heat.

In some embodiments, the ablation catheter 3120 comprises multiplethermal transfer members 3145 (for example, heat shunt disks ormembers). For example, according to some embodiments, such additionalheat transfer members may be positioned proximal of thermal transfermember 3145 and may comprise one or more fins, pins and/or other membersthat are in thermal communication with the irrigation conduit 3150extending through an interior of the ablation catheter. Accordingly, aswith the thermal transfer members 3145 positioned in contact with theelectrode members 3130, 3135 heat can be transferred and thus removed ordissipated, from other energy delivery members or electrodes, theadjacent portions of the catheter and/or the adjacent tissue of thesubject via these additional heat transfer members (for example, heatshunting members). In other embodiments, ablation catheters do notcomprise any thermal transfer members.

In some embodiments, for any of the ablation catheters disclosed hereinor variations thereof, one or more of the thermal transfer members (forexample, heat shunting members) that facilitate the heat transfer to aheat exchange chamber (for example, irrigation conduit) of the catheterare in direct contact with the electrode members and/or the heatexchange chamber. However, in other embodiments, one or more of thethermal transfer members do not contact the electrode members and/or theirrigation conduit. Thus, in such embodiments, the thermal transfermembers are in thermal communication with the electrode members orsingle electrode and/or irrigation conduit, but not in physical contactwith such components. For example, in some embodiments, one or moreintermediate components, layers, coatings and/or other members arepositioned between a thermal transfer member (for example, heat shuntingmember) and the electrode (or other ablation member) and/or theirrigation conduit. In some embodiments, irrigation is not used at alldue to the efficiency of the thermal transfer members. For example,where multiple levels or stacks of thermal transfers are used, the heatmay be dissipated over a larger area along the length of the ablationcatheter. Additional details regarding function and features of thermaltransfer members (for example, heat shunting members) are providedherein. The features of the various embodiments disclosed therein (forexample, of thermal shunt systems and members) may be implemented in anyof the embodiments of the medical instruments (for example, ablationcatheters) disclosed herein.

As best shown in FIGS. 18C, 18E and 18F, the temperature-measurementdevices 3125 are thermally insulated from the electrode members 3130,3135 by tubing 3160 and/or air gaps. In some embodiments, the tubing3160 extends along an entire length (and beyond in some embodiments) ofthe electrode members 3130, 3135 such that no portion of the electrodemember is in contact with the temperature-measurement devices 3125,thereby isolating the temperature measurements from the thermal effectsof the electrode members. The outer tubing 3160 of thetemperature-measurement devices may comprise an insulating materialhaving low thermal conductivity (for example, polyimide, ULTEM™,polystyrene or other materials having a thermal conductivity of lessthan about 0.5 W/mPK). The tubing 3160 is substantially filled with airor another gas having very low thermal conductivity. The distal tip 3165of the temperature-sensing device (for example, the portion where thetemperature is sensed) may comprise an epoxy polymer covering or casingfilled with a highly conductive medium (for example, nanotubes comprisedof graphene, carbon or other highly thermally conductive materials orfilms) to increase thermal conduction at a head of thetemperature-measurement device where temperature is measured. In someembodiments, the distal tip 3165 comprises an epoxy cap having a thermalconductivity that is at least 1.0 W/mPK. The epoxy may comprise metallicpaste (for example, containing aluminum oxide) to provide the enhancedthermal conductivity. In some embodiments, the distal tip 3165 or capcreates an isothermal condition around the temperature-measurementdevice 3125 that is close to the actual temperature of tissue in contactwith the temperature-measurement device. Because the distal tip 3165 ofeach temperature-measurement device 3125 is isolated from thermalconductive contact with the electrode member(s), it retains thisisothermal condition, thereby preventing or reducing the likelihood ofdissipation by the thermal mass of the electrode member(s). FIGS. 18Eand 18F illustrate a perspective view and a cross-sectional view,respectively, of a distal portion of an ablation catheter showingisolation of the distal temperature-measurement devices from anelectrode tip, according to one embodiment. As shown, the distaltemperature measurement devices 3125A may be surrounded by air gaps orpockets 3162 and/or insulation. The outer tubing 3160 may comprise aninsulation sleeve that extends along the entire length, or at least aportion of the length, of the distal electrode member 3130. The sleevemay extend beyond the distal electrode member 3130 or even to or beyondthe proximal electrode member 3135.

The electrode member(s) (for example, the distal electrode 3130) can beelectrically coupled to an energy delivery module (for example, energydelivery module 40 of FIG. 1). As discussed herein, the energy deliverymodule 40 can comprise one or more components or features, such as, forexample, an energy generation device 42 that is configured toselectively energize and/or otherwise activate the energy deliverymembers (for example, RF electrodes), one or more input/output devicesor components, a processor (for example, a processing or control unit)that is configured to regulate one or more aspects of the treatmentsystem, a memory and/or the like. Further, such a module can beconfigured to be operated manually or automatically, as desired orrequired.

The temperature-measurement devices 3125 can be coupled to one or moreconductors (for example, wires, cables, etc.) that extend along thelength of the ablation catheter 3120 and communicate the temperaturesignals back to a processing device (for example, processor 46 ofFIG. 1) for determining temperature measurements for each of thetemperature-measurement devices, as will be discussed in greater detailbelow.

According to some embodiments, the relative length of the differentelectrodes or electrode members 3130, 3135 can vary. For example, thelength of the proximal electrode member 3135 can be between 1 to 20times (for example, 1-2, 2-3, 3-4, 4-5, 5-6, 6-7, 7-8, 8-9, 9-10, 10-11,11-12, 12-13, 13-14, 14-15, 15-16, 16-17, 17-18, 18-19, 19-20, valuesbetween the foregoing ranges, etc.) the length of the distal electrodemember 3130, as desired or required. In yet other embodiments, thelengths of the distal and proximal electrode members 3130, 3135 areabout equal. In some embodiments, the distal electrode member 3130 islonger than the proximal electrode member 3135 (for example, by 1 to 20times, such as, for example, 1-2, 2-3, 3-4, 4-5, 5-6, 6-7, 7-8, 8-9,9-10, 10-11, 11-12, 12-13, 13-14, 14-15, 15-16, 16-17, 17-18, 18-19,19-20, values between the foregoing ranges, etc.).

In some embodiments, the distal electrode member 3130 is 0.5 mm long. Inother embodiments, the distal electrode member 130 is between 0.1 mm and1 mm long (for example, 0.1-0.2, 0.2-0.3, 0.3-0.4, 0.4-0.5, 0.5-0.6,0.6-0.7, 0.7-0.8, 0.8-0.9, 0.9-1 mm, values between the foregoingranges, etc.). In other embodiments, the distal electrode member 3130 isgreater than 1 mm in length, as desired or required. In someembodiments, the proximal electrode member 3135 is 2 to 4 mm long (forexample, 2-2.5, 2.5-3, 3-3.5, 3.5-4 mm, lengths between the foregoing,etc.). However, in other embodiments, the proximal electrode member 3135is greater than 4 mm (for example, 4-5, 5-6, 6-7, 7-8, 8-9, 9-10 mm,greater than 10 mm, etc.) or smaller than 1 mm (for example, 0.1-0.5,0.5-1, 1-1.5, 1.5-2 mm, lengths between the foregoing ranges, etc.), asdesired or required. In embodiments where the split electrodes arelocated on catheter shafts, the length of the electrode members can be 1to 5 mm (for example, 1-2, 2-3, 3-4, 4-5 mm, lengths between theforegoing, etc.). However, in other embodiments, the electrode memberscan be longer than 5 mm (for example, 5-6, 6-7, 7-8, 8-9, 9-10, 10-15,15-20 mm, lengths between the foregoing, lengths greater than 20 mm,etc.), as desired or required.

The electrode member(s) may be energized using one or more conductors(for example, wires, cables, etc.). For example, in some arrangements,the exterior of the irrigation conduit 3150 comprises and/or isotherwise coated with one or more electrically conductive materials (forexample, copper, other metal, etc.). Thus, the conductor can be placedin contact with such a conductive surface or portion of the irrigationconduit 3150 to electrically couple the electrode member(s) to an energydelivery module. However, one or more other devices and/or methods ofplacing the electrode member(s) in electrical communication with anenergy delivery module can be used. For example, one or more wires,cables and/or other conductors can directly or indirectly couple to theelectrode member(s), without the use of the irrigation conduit.

The use of a split tip design can permit a user to simultaneously ablateor otherwise thermally treat targeted tissue and map (for example, usinghigh-resolution mapping) in a single configuration. Thus, such systemscan advantageously permit precise high-resolution mapping (for example,to confirm that a desired level of treatment occurred) during aprocedure. In some embodiments, the split tip design that includes twoelectrode members or electrode portions 3130, 3135 can be used to recorda high-resolution bipolar electrogram. For such purposes, the twoelectrodes or electrode portions can be connected to the inputs of anelectrophysiology (EP) recorder. In some embodiments, a relatively smallseparation distance (for example, gap G) between the electrode membersor electrode portions 3130, 3135 enables high-resolution mapping. Thefeatures of any of the embodiments disclosed therein may be implementedin any of the embodiments disclosed herein.

In some embodiments, a medical instrument (for example, a catheter) 3120can include three or more electrode members or electrode portions (forexample, separated by gaps), as desired or required. According to someembodiments, regardless of how many electrodes or electrode portions arepositioned along a catheter tip, the electrode members or electrodeportions 3130, 3135 are radiofrequency electrodes and comprise one ormore metals, such as, for example, stainless steel, platinum,platinum-iridium, gold, gold-plated alloys and/or the like.

According to some embodiments, the electrode members or electrodeportions 3130, 3135 are spaced apart from each other (for example,longitudinally or axially) using the gap (for example, an electricallyinsulating gap) 3131. In some embodiments, the length of the gap 3131(or the separation distance between adjacent electrode members orelectrode portions) is 0.5 mm. In other embodiments, the gap orseparation distance is greater or smaller than 0.5 mm, such as, forexample, 0.1-1 mm (for example, 0.1-0.2, 0.2-0.3, 0.3-0.4, 0.4-0.5,0.5-0.6, 0.6-0.7, 0.7-0.8, 0.8-0.9, 0.9-1.0 mm, values between theforegoing ranges, less than 0.1 mm, greater than 1 mm, etc.), as desiredor required

According to some embodiments, a separator is positioned within the gap3131 between the adjacent electrode members or electrode portions 3130,3135. The separator can comprise one or more electrically insulatingmaterials, such as, for example, Teflon, polyetheretherketone (PEEK),diamond, epoxy, polyetherimide resins (for example, ULTEM™), ceramicmaterials, polyimide and the like. As shown in FIGS. 18A-18C and19A-19C, the separator may comprise a portion of the thermal transfermember 3145 extending within the gap 3131.

As noted above with respect to the gap 3131 separating the adjacentelectrode members or electrode portions, the insulating separator can be0.5 mm long. In other embodiments, the length of the separator can begreater or smaller than 0.5 mm (for example, 0.1-0.2, 0.2-0.3, 0.3-0.4,0.4-0.5, 0.5-0.6, 0.6-0.7, 0.7-0.8, 0.8-0.9, 0.9-1.0 mm, values betweenthe foregoing ranges, less than 0.1 mm, greater than 1 mm, etc.), asdesired or required.

According to some embodiments, to ablate or otherwise heat or treattargeted tissue of a subject successfully with the split tip electrodedesign, such as the ones depicted in FIGS. 18A-18C and 19A-19C, the twoelectrode members or electrode portions 3130, 3135 are electricallycoupled to each other at the RF frequency. Thus, the two electrodemembers or electrode portions can advantageously function as a singlelonger electrode at the RF frequency. Additional details regardingfunction and features of a split-tip electrode design are providedherein.

FIGS. 19A-19C illustrate a distal portion of closed-irrigation ablationcatheters 3220 having multiple temperature-measurement devices 3225,according to various embodiments. The embodiment of the ablationcatheter 3220A of FIG. 19A comprises a dome-shaped tip electrode member3230 similar to the ablation catheter 3120A of FIG. 18A. The embodimentof the ablation catheter 3220B of FIGS. 19B and 19C comprises a flat tipelectrode member similar to the ablation catheter 3120B of FIGS. 18B and18C. The ablation catheters 3220A and 3220B include similar componentsand features as those described above in connection with FIGS. 18A-18C.For example, temperature-measurement devices 3225 correspond totemperature-measurement devices 3125, electrode members 3230, 3235correspond to electrode members 3130, 3135, thermal transfer member 3245corresponds to thermal transfer member 3145 and irrigation conduit 3250corresponds to irrigation conduit 3150. Accordingly, these features willnot be described again in connection with FIGS. 19A-19C. The ablationcatheter 3220 does not include irrigation ports because it operates as aclosed irrigation device.

The ablation catheter 3220 comprises two lumens 3265 within theirrigation conduit 3250, an inlet lumen (for example, fluid deliverychannel) 3265A and an outlet lumen (for example, return channel) 3265B.As illustrated in the cross-sectional view of FIG. 19C, the outlet ofthe inlet lumen 3265A and the inlet of the outlet lumen 3265B terminateat spaced-apart locations within the irrigation conduit 3250. The outletof the inlet lumen 3265A terminates within the distal electrode member3230 or adjacent to a proximal end surface of the distal electrodemember 3230. The inlet of the outlet lumen terminates proximal to theproximal end of the proximal electrode member 3235. The offset spacingof the distal ends of the lumens 3265 advantageously induces turbulence,vortexing or other circulating fluid motions or paths within theirrigation conduit, thereby facilitating enhanced cooling by circulatingthe fluid to constantly refresh or exchange the fluid in contact withthe thermal transfer member 3245 and/or electrode members.

In accordance with several embodiments, ablation catheters havingmultiple temperature-measurement devices do not require a split-tipelectrode design and/or thermal transfer members. FIG. 20 illustrates aperspective view of a distal portion of an open-irrigated ablationcatheter 3320 that does not include a split-tip electrode design or athermal transfer member. The ablation catheter 3320 comprises a first(for example, distal) plurality of temperature-measurement devices 3325Aand a second (for example, proximal) plurality oftemperature-measurement devices 3325B. The temperature-measurementdevices 3325 comprise similar features, properties, materials, elementsand functions as the temperature-measurement devices 3125, 3225 (FIGS.18A-19C). The ablation catheter 3320 may comprise or consist of a singleunitary tip electrode 3330. The tip electrode 3330 may compriseapertures, slots, grooves, bores or openings for thetemperature-measurement devices 3325 at their respective spaced-apartlocations. As shown in FIG. 20, the proximal temperature-measurementdevices 3325B are positioned distal but adjacent to the proximal edge ofthe tip electrode 3330. The proximal temperature-measurement devices3325B could be positioned within 1 mm of the proximal edge (for example,within 0.9, 0.8, 0.7, 0.6, 0.5, 0.4, 0.3, 0.2, 0.1 mm, depending on thelength of the tip electrode 330). In other embodiments, the proximaltemperature-measurement devices 3325B are positioned proximal of theproximal edge of the tip electrode 3330 and within the same distance asdescribed above of distal placement. In various embodiments, thetemperature-measurement devices are positioned at or near the proximaland distal edges of the electrode or split-tip electrode assemblybecause those locations tend to be the hottest. Based on manufacturingtolerances, these temperature measurement devices may be embedded at theproximal or distal edge of the electrode 3330. Accordingly, positioningof the temperature-measurement devices at or near these locations mayfacilitate prevention, or reduced likelihood, of overheating or char orthrombus formation. Additionally, such temperature-measurement deviceplacement offers the ability to monitor tissue temperature duringirrigated ablation.

In some embodiments, epoxy comprising a conductive medium (such asgraphene or other carbon nanotubes) may be blended in to the distaltubing (typically formed of plastic) of the ablation catheter shaft andthe distal tubing of the ablation catheter itself may function as athermal transfer. In some embodiments, the addition of the conductiveepoxy could increase the thermal conductivity of the distal tubing by2-3 times or more. These conductive tubing features and other featuresdescribed in connection with FIG. 20 may be used in connection with theablation catheters 3120, 3220 as well.

FIGS. 21A and 21B schematically illustrate a distal portion of anopen-irrigated ablation catheter 3420 in perpendicular contact andparallel contact, respectively, with tissue and formation of thermallesions by delivering energy to the tissue using the ablation catheter3420. In accordance with several embodiments, the ablation cathetershaving multiple temperature-measurement devices described hereinadvantageously facilitate determination of, among other things: anorientation of the distal tip of the ablation catheter with respect tothe tissue, an estimated peak temperature within the thermal lesion,and/or a location of the peak temperature zone within the thermallesion.

As mentioned above, the temperature-measurement devices 3425 may send ortransmit signals to a processing device (for example, processor 46 ofFIG. 1). The processing device may be programmed to execute instructionsstored on one or more computer-readable storage media to determinetemperature measurements for each of the temperature-measurement devices3425 and to compare the determined temperature measurements with eachother to determine an orientation of the distal tip of the ablationcatheter with respect to the tissue based, at least in part, on thecomparison. The processing device may select an orientation from one ofparallel, perpendicular, or angled (for example, skewed or oblique)orientations.

For example, if the temperature measurements received from the distaltemperature-measurement devices are all greater (for example, hotter)than the temperature measurements received from the proximaltemperature-measurement devices, then the processor may determine thatthe orientation is perpendicular. If the temperature measurementsreceived from at least one proximal temperature-measurement device andat least one corresponding distal temperature-measurement device aresimilar, then the processor may determine that the orientation isparallel.

As other examples, for embodiments using three temperature-measurementdevices, if two of three proximal temperature-measurement devicesgenerate much lower (and generally equal) temperature measurements thanthe third proximal-temperature measurement device, then the processingdevice may determine that the orientation is parallel. For embodimentsusing three temperature-measurement devices, if the temperaturemeasurements received from a first proximal temperature-measurementdevice are appreciably greater than temperature measurements from asecond proximal temperature-measurement device and if the temperaturemeasurements received from the second proximal temperature-measurementdevice are appreciably greater than temperature measurements receivedfrom a third proximal temperature-measurement device, then theprocessing device may determine that the orientation is neither parallelnor perpendicular but skewed at an angle. In some embodiments,orientation may be confirmed using fluoroscopic imaging, ICE imaging orother imaging methods or techniques.

In some embodiments, the determined orientation may be output on adisplay (for example, a graphical user interface) for visibility by auser. The output may comprise one or more graphical images indicative ofan orientation or alphanumeric information indicative of the orientation(for example, a letter, word, phrase or number). The processing devicemay apply correction factors to the temperature measurements receivedfrom the temperature-measurement devices based on the determinedorientation in order to generate more accurate estimates of a peaktemperature of the thermal lesion. For example, if a perpendicularorientation is determined, then a correction factor or functioncorresponding to the distal temperature-measurement devices may beapplied to determine the estimated peak temperature.

The processing device may comprise a temperature acquisition module anda temperature processing module, in some embodiments. The temperatureacquisition module may be configured to receive as input temperaturesignals (for example, analog signals) generated by each of thetemperature-measurement devices. The input signals may be continuouslyreceived at prescribed time periods. The temperature acquisition modulemay be configured to covert analog signals into digital signals. Thetemperature processing module may receive the digital signals outputfrom the temperature acquisition module and apply correction factors orfunctions to them to estimate a hottest tissue temperature, a peaktemperature or a peak temperature in a thermal lesion created in thevicinity of the electrode or other energy delivery member(s). Thetemperature processing module may compute a composite temperature fromthe temperature-measurement devices (for example, thermocouples) basedon the following equation:Tcomp(t)=k(t)*f(TC1(t),TC2(t), . . . ,TCn(t));

where Tcomp is the composite temperature, k is the k function orcorrection or adjustment function, f is a function of the thermocouplereadings TCi, i=1 to n. The k function may comprise a function over timeor a constant value. For example, a k function may be defined asfollows:k(t)=e ^((−t/τ)) +k _(final)*(1−e ^((−t/τ)));

where τ is a time constant representative of the tissue time constantand k_(final) is a final value of k, as per a correction factor orfunction, such as described in connection with FIG. 22A below.

The temperature processing module may also be configured to determine anorientation of a distal tip of a medical instrument with respect totissue, as described above. The processing device may further comprisean output module and a feedback/monitoring module. The output module maybe configured to generate output for display on a display, such as thevarious outputs described herein. The feedback/monitoring modules may beconfigured to compare measured temperature values against apredetermined setpoint temperature or maximum temperature and toinitiate action (for example, an alert to cause a user to adjust poweror other ablation parameters or automatic reduction in power level ortermination of energy delivery (which may be temporary until thetemperature decreases below the setpoint temperature). In variousembodiments, the setpoint, or maximum, temperature is between 50 and 90degrees Celsius (for example, 50, 55, 60, 65, 70, 75, 80, 85 degreesCelsius).

In accordance with several embodiments, there is a proportionalrelationship between the temperature gradient determined by thetemperature-measurement devices and the peak temperature of the lesion.From this relationship, a function or correction factor is generated orapplied based on numerical modeling (for example, finite element methodmodeling techniques) and/or measurements stored in a look-up table toadjust or correct from the thermal gradient identified by thetemperature-measurement devices to determine the peak temperature. Thethermal gradient of an open-irrigated lesion is such that the lesionsurface is a little bit cooled and the peak temperature zone is deeper.The further the temperature-measurement devices can be buried intotissue, the better or more accurate the proportional relationship may bebetween the thermal gradient determined by the temperature-measurementdevices and the peak temperature. For example, the thermal gradient canbe estimated as:ΔT/Δd=(T _(distal) −T _(proximal))/TC_separation distanceIn other words, the temperature spatial gradient is estimated as thedifference in temperature between the distal and proximaltemperature-measurement devices divided by the distance between thedistal and proximal temperature-measurement devices. The peak tissuetemperature (where peak can be a hill or a valley) can then be estimatedas:T _(peak) =ΔT/Δd*T _(peak_dist) +T _(distal)

The processing device may also determine an estimated location of thepeak temperature zone of the thermal lesion based, at least in part, onthe determined orientation and/or the temperature measurements. Forexample, for a perpendicular orientation, the peak temperature locationmay be determined to be horizontally centered in the thermal lesion. Insome embodiments, the processor may be configured to output informationindicative of the peak temperature location on a display (for example, agraphical user interface). The information may include textualinformation and/or one or more graphical images.

FIG. 22A is a graph illustrating that temperature measurements obtainedfrom the temperature-measurement devices may be used to determine a peaktemperature by applying one or more analytical correction factors orfunctions to the temperature measurements (for example, using numericalmodeling approximations or look-up tables). As shown in FIG. 6A, asingle correction factor or function (k) may be applied to each of thedistal temperature-measurement devices to determine the peaktemperature. In some embodiments, different correction factors orfunctions may be applied to each individual temperature-measurementdevice or to subsets of the groups of temperature-measurement devicesdepending on a determined orientation or on a comparison of thetemperature measurements obtained by the temperature-measurementdevices, thereby providing increased accuracy of peak temperature andpeak temperature zone location. The increased accuracy of peaktemperature and peak temperature zone location may advantageously resultin safer and more reliable ablation procedures because the ablationparameters may be adjusted based on feedback received by the processingunit from the temperature-measurement devices. In accordance withseveral embodiments, peak temperatures at a depth beneath the tissuesurface are accurately estimated without requiring microwave radiometry.With reference to FIG. 22A, the peak tissue temperature can be estimatedas follows:T _(peak)(t)=e ^((−t/τ)) +k*(1−e ^((−t/τ)))*max(TCi(t));

where i spans the range of temperature-measurement devices, withmax(TCi(t)) representing the maximum temperature reading of thetemperature-measurement devices at time t. For example, FIG. 22B showsan implementation of the above formula. Trace 1 shows the estimated peaktissue temperature (T_(peak)) at a constant k value of 1.8 and a t valueof 1, whereas Traces 2, 3 and 4 show the actual tissue temperaturesmeasured at 1 mm, 3 mm and 5 mm, respectively, from the tissue surfaceusing tissue-embedded infrared probes. As seen, the estimated peaktissue temperature (T_(peak)) of Trace 1 tracks well the actual peaktissue temperature measured at 1 mm depth (Trace 2).

In another embodiment, a predictive model-based approach utilizing thebioheat equation may be utilized to estimate peak tissue temperature. Arecursive algorithm for determining the temperature T at a time point n,at a single point in a volume during treatment (for example, RFablation) may be defined as follows:

$T_{n} = \frac{{\frac{\rho \cdot C}{dt} \cdot T_{n - 1}} + {W_{e} \cdot C \cdot T_{a}} + {P \cdot N}}{\frac{\rho \cdot C}{dt} + {W_{e} \cdot C}}$where T_(n) is the current temperature, T_(n-1) is the previoustemperature, t is time, ρ is the tissue density, C is the specific heatof tissue, T_(a) is the core arterial temperature, W_(e) is an effectiveperfusion rate, and P·N provides an estimate of the volumetric powerdeposited in tissue. The above equation can be formulated at variousspatial locations, including the temperature-measurement devicelocation(s) as well as the location of peak temperature (for example,hot spot). By utilizing this model at different locations, along withcalibration to determine the model parameters, mapping techniques can beutilized to predict the temperature at one spatial location usingmeasurement data from the other spatial location.

In some embodiments, the processing device is configured to output thepeak temperature or other output indicative of the peak temperature on adisplay (for example, a graphical user interface). The output maycomprise alphanumeric information (for example, the temperature indegrees), one or more graphical images, and/or a color indication. Insome embodiments, the processor may generate an output configured toterminate energy delivery if the determined peak temperature is above athreshold or maximum temperature. The output may comprise a signalconfigured to cause automatic termination of energy delivery or maycomprise an alert (audible and/or visual) to cause a user to manuallyterminate energy delivery.

In various embodiments, ablation parameters may be adjusted based ontemperature measurements received from the temperature-measurementdevices. The ablation parameters may comprise, among other things,duration of ablation, power modulation, contact force, target orsetpoint temperature, a maximum temperature. The processor 46 (FIG. 1)may be configured to send control signals to the energy delivery module40 based on the temperature measurements (and other measurements orestimations derived or otherwise determined therefrom) received from thetemperature-measurement devices.

In one embodiment, the energy delivery module 40 (FIG. 1) may be set torun in a temperature control mode, wherein radiofrequency energy of acertain power level is delivered and a maximum temperature is identifiedwhich cannot be exceeded. Each of the temperature-measurement devicesmay be monitored (either simultaneously or via toggled queries) on aperiodic or continuous basis. If the maximum temperature is reached orexceeded, as determined by temperature measurements received from any ofthe temperature-measurement devices of the ablation catheters describedherein, control signals may be sent to the energy delivery module toadjust ablation parameters (for example, reduction in power level) toreduce the temperature or to terminate energy delivery (temporarily orotherwise) until the temperature is reduced below the maximumtemperature. The adjustments may be effected for example by aproportional-integral-derivative controller (PID controller) of theenergy delivery module 40. In another embodiment, the energy deliverymodule 40 may be set to run in a power control mode, in which a certainlevel of power is applied continuously and the temperature measurementsreceived from each of the temperature-measurement devices are monitoredto make sure a maximum temperature is not exceeded. In some embodiments,a temperature-controlled mode comprises specifying a setpointtemperature (for example, 70 degrees Celsius, 75 degrees Celsius, 80degrees Celsius, and then adjusting power or other parameters tomaintain temperature at, below or near the setpoint temperature, asdetermined from the temperature measurements received from each of thetemperature-measurement devices.

Table 1 below shows examples of ablation parameters used in various testablation procedures using an embodiment of an ablation catheterdescribed herein.

TABLE 1 Max Tissue Blood flow Irrigation Power Temp Lesion width Lesiondepth Impedance Orientation (cm/s) (ml/min) (W) (° C.) (mm) (mm) (Ohms)Parallel 0.5 15 13.3 91.7 9.8 5.2 85 Parallel 25 15 15.8 94.9 9.2 5.4 85Parallel 0.5 0 8.6 98.8 11.2 4.7 85 Parallel 25 0 14.9 94.8 10.0 5.3 85Perpend. 0.5 15 16.8 99.4 11 5.6 83 Perpend. 25 15 18.1 99.9 10.3 5.8 83Perpend. 0.5 0 10.4 97.9 10.3 4.8 83 Perpend. 25 0 16.9 95.7 9.3 5.3 83

As can be seen from the data in Table 1, the maximum tissue temperatureand lesion sizes remained relatively constant with or without irrigationand/or with or without significant blood flow by modulating the power.The multi-variant or multiple temperature-measurement device systemaccording to embodiments of this invention ensures appropriate tissueablation under different electrode-tissue orientations. As explainedabove, the electrode-tissue orientation can be determined based onreadings from the multiple temperature-measurement devices. If bothproximal and distal temperatures become dominant, then the electrodeorientation is estimated or indicated to be parallel to tissue.Similarly, when the distal temperatures are dominant, then the electrodeorientation is inferred, estimated and/or indicated to be perpendicularto tissue. Combinations of proximal and distal dominant temperatures mayprovide indications for oblique electrode orientations. FIG. 23Aillustrates a plot of temperature data from the multipletemperature-measurement devices (for example, thermocouples) that areindicative of a perpendicular orientation and FIG. 23B illustrates aplot of temperature data from the multiple temperature-measurementdevices (for example, thermocouples) that are indicative of an obliqueorientation.

Contact Sensing

According to some embodiments, various implementations of electrodes(for example, radiofrequency or RF electrodes) that can be used forhigh-resolution mapping and radiofrequency ablation are disclosedherein. For example, as discussed in greater detail herein, an ablationor other energy delivery system can comprise a high-resolution, orcombination electrode, design, wherein the energy delivery member (forexample, radiofrequency electrode, laser electrode, microwavetransmitting electrode) comprises two or more separate electrodes orelectrode members or portions. As also discussed herein, in someembodiments, such separate electrodes or electrode portions can beadvantageously electrically coupled to each other (for example, tocollectively create the desired heating or ablation of targeted tissue).In various embodiments, the combination electrode, or split-tip, designmay be leveraged to determine whether or not one or more portions of theelectrodes or other energy delivery members are in contact with tissue(for example, endocardial tissue) and/or whether or not contacted tissuehas been ablated (for example, to determine whether the tissue is viableor not).

Several embodiments of the invention are particularly advantageousbecause they include one, several or all of the following benefits: (i)confirmation of actual tissue contact that is easily ascertainable; (ii)confirmation of contact with ablated vs. unablated (viable) tissue thatis easily ascertainable; (iii) low cost, as the invention does notrequire any specialized sensor; (iv) does not require use of radiometry;(v) provides multiple forms of output or feedback to a user; (vi)provides output to a user without requiring the user to be watching adisplay; and/or (vii) provides safer and more reliable ablationprocedures.

With reference to FIG. 1, according to some embodiments, the deliverymodule 40 includes a processor 46 (for example, a processing or controldevice) that is configured to regulate one or more aspects of thetreatment system 10. The delivery module 40 can also comprise a memoryunit or other storage device 48 (for example, non-transitory computerreadable medium) that can be used to store operational parameters and/orother data related to the operation of the system 10. In someembodiments, the processor 46 comprises or is in communication with acontact sensing and/or a tissue type detection module or subsystem. Thecontact sensing subsystem or module may be configured to determinewhether or not the energy delivery member(s) 30 of the medicalinstrument 20 are in contact with tissue (for example, contactsufficient to provide effective energy delivery). The tissue typedetection module or subsystem may be configured to determine whether thetissue in contact with the one or more energy delivery member(s) 30 hasbeen ablated or otherwise treated. In some embodiments, the system 10comprises a contact sensing subsystem 50. The contact sensing subsystem50 may be communicatively coupled to the processor 46 and/or comprises aseparate controller or processor and memory or other storage media. Thecontact sensing subsystem 50 may perform both contact sensing and tissuetype determination functions. The contact sensing subsystem 50 may be adiscrete, standalone sub-component of the system (as shown schematicallyin FIG. 1) or may be integrated into the energy delivery module 40 orthe medical instrument 20. Additional details regarding a contactsensing subsystem are provided below.

In some embodiments, the processor 46 is configured to automaticallyregulate the delivery of energy from the energy generation device 42 tothe energy delivery member 30 of the medical instrument 20 based on oneor more operational schemes. For example, energy provided to the energydelivery member 30 (and thus, the amount of heat transferred to or fromthe targeted tissue) can be regulated based on, among other things, thedetected temperature of the tissue being treated, whether the tissue isdetermined to have been ablated, or whether the energy delivery member30 is determined to be in contact (for example, “sufficient” contact, orcontact above a threshold level) with the tissue to be treated.

With reference to FIG. 24, the distal electrode 30A may be energizedusing one or more conductors (for example, wires, cables, etc.). Forexample, in some arrangements, the exterior of an irrigation tubecomprises and/or is otherwise coated with one or more electricallyconductive materials (for example, copper, other metal, etc.). Thus, theone or more conductors can be placed in contact with such a conductivesurface or portion of the irrigation tube to electrically couple theelectrode or electrode portion 30A to an energy delivery module (forexample, energy delivery module 40 of FIG. 1). However, one or moreother devices and/or methods of placing the electrode or electrodeportion 30A in electrical communication with an energy delivery modulecan be used. For example, one or more wires, cables and/or otherconductors can directly or indirectly couple to the electrodes, withoutthe use of the irrigation tube. The energy delivery module may beconfigured to deliver electromagnetic energy at frequencies useful fordetermining contact (for example, between 5 kHz and 1000 kHz).

FIG. 24 schematically illustrates one embodiment of a combination, orsplit-tip, electrode assembly that can be used to perform contactsensing or determination by measuring the bipolar impedance between theseparated electrodes or electrode portions 30A, 30B at differentfrequencies. Resistance values may be determined from voltage andcurrent based on Ohm's Law: Voltage=Current*Resistance, or V=IR.Accordingly, resistance equals voltage divided by current. Similarly, ifthe impedance between the electrodes is complex, the complex voltage andcurrent may be measured and impedance (Z) determined byV_complex=I_complex*Z_complex. In this case, both magnitude and phaseinformation for the impedance can be determined as a function offrequencies. The different frequencies may be applied to the split-tipelectrode assembly by an energy delivery module (for example, by energygeneration device 42 of energy delivery module 40 of FIG. 1) or acontact sensing subsystem (such as contact sensing subsystem 50 ofsystem 10 of FIG. 1). Because the voltage and current values may beknown or measured, the resistance and/or complex impedance values can bedetermined from the voltage and current values using Ohm's Law. Thus,the impedance values may be calculated based on measured voltage and/orcurrent values in accordance with several embodiments rather thandirectly obtaining impedance measurements.

FIG. 25A is a plot showing resistance, or magnitude impedance, values ofblood (or a blood/saline combination) and of cardiac tissue across arange of frequencies (5 kHz to 1000 kHz). The impedance values arenormalized by dividing the measured impedance magnitude by the maximumimpedance magnitude value. As can be seen, the normalized impedance ofblood (or a blood/saline combination) does not vary significantly acrossthe entire range of frequencies. However, the normalized impedance ofcardiac tissue does vary significantly over the range of frequencies,forming a roughly “s-shaped” curve.

In one embodiment, resistance or impedance measurements can be obtainedat two, three, four, five, six or more than six different discretefrequencies within a certain range of frequencies. In severalembodiments, the range of frequencies may span the range of frequenciesused to ablate or otherwise heat targeted tissue. For example,resistance or impedance measurements may be obtained at two differentfrequencies f₁ and f₂ within the range of frequencies, where f₂ isgreater than f₁. Frequency f₁ may also be below the ablation frequencyrange and f₂ may be above the ablation frequency range. In otherembodiments, f₁ and/or f₂ can be in the range of ablation frequencies.In one embodiment, f₁ is 20 kHz and f₂ is 800 kHz. In variousembodiments, f₁ is between 10 kHz and 100 kHz and f₂ is between 400 kHzand 1000 kHz. By comparing the impedance magnitude values obtained atthe different frequencies, a processing device (for example, a contactsensing subsystem or module coupled to or executable by processor 46 ofFIG. 1) can determine whether or not the electrode portion 30A is incontact with issue (for example, cardiac tissue) upon execution ofspecific program instructions stored on a non-transitorycomputer-readable storage medium.

For example, if the ratio r of an impedance magnitude value obtained atthe higher frequency f₂ to the impedance magnitude value obtained at thelower frequency f₁ is smaller than a predetermined threshold, theprocessing device may determine that the electrode portion 30A is incontact with cardiac tissue or other target region (for example, uponexecution of specific program instructions stored on a non-transitorycomputer-readable storage medium). However, if the ratio r of animpedance magnitude value obtained at the higher frequency f₂ to theimpedance magnitude value obtained at the lower frequency f₁ is greaterthan a predetermined threshold, the processing device may determine thatthe electrode portion 30A is not in contact with cardiac tissue butinstead is in contact with blood or a blood/saline combination. Thecontact determinations may be represented as follows:

${\frac{r_{f\; 2}}{r_{f\; 1}} < {threshold}} = {CONTACT}$${\frac{r_{f\; 2}}{r_{f\; 1}} > {threshold}} = {{NO\_}{CONTACT}}$

In various embodiments, the predetermined threshold has a value between0.2 and less than 1 (for example, between 0.2 and 0.99, between 0.3 and0.95, between 0.4 and 0.9, between 0.5 and 0.9 or overlapping rangesthereof).

In various embodiments, resistance or impedance measurements areperiodically or continuously obtained at the different frequencies (forexample, two, three, four or more different frequencies) by utilizing asource voltage or current waveform that is a multi-tone signal includingthe frequencies of interest, as shown in FIG. 25B. The multi-tone signalor waveform may be sampled in the time-domain and then transformed tothe frequency domain to extract the resistance or impedance at thefrequencies of interest, as shown in FIG. 25C. In some embodiments,measurements or determinations indicative of contact may be obtained inthe time domain instead of the frequency domain. Signals or waveformshaving different frequencies may be used. In accordance with severalembodiments, performing the contact sensing operations is designed tohave little or no effect on the electrogram (EGM) functionality of thecombination, or split-tip, electrode assembly. For example, common modechokes and DC blocking circuits may be utilized in the path of theimpedance measurement circuitry as shown in FIG. 25D. The circuitry mayalso include a reference resistor R to limit the maximum current flow tothe patient, as well as dual voltage sampling points V1 and V2 toenhance the accuracy of the impedance measurements. Additionally, alow-pass filter circuit (with, for example, a cut-off frequency of 7kHz) may be utilized in the path of the EGM recording system, as shownin FIG. 4D. In several embodiments, all or portions of the circuitryshown in FIG. 25D are used in a contact sensing subsystem, such ascontact sensing subsystem 50 of FIG. 1 or contact sensing subsystem 4650of FIG. 27. The frequencies used for contact sensing may be at leastgreater than five times, at least greater than six times, at leastgreater than seven times, at least greater than eight times, at leastgreater than nine times, at least greater than ten times the EGMrecording or mapping frequencies. The contact sensing subsystem may becontrolled by a processing device including, for example, ananalog-to-digital converter (ADC) and a microcontroller (MCU). Theprocessing device may be integral with the processing device 46 of FIG.1 or may be a separate, stand-alone processing device. If a separateprocessing device is used, the separate processing device may becommunicatively coupled to the processing device 46 of FIG. 1.

In various embodiments, resistance or impedance measurements (forexample, total impedance or component parts of complex impedance) areperiodically or continuously obtained at the different frequencies (forexample, two or three different frequencies) by switching between thedifferent frequencies. In accordance with several embodiments,performing the contact sensing operations may be designed to have littleor no effect on the electrogram (EGM) functionality of the combinationelectrode, or split-tip, assembly. Accordingly, switching between thedifferent frequencies may advantageously be synched to zero crossings ofan AC signal waveform, as illustrated in FIG. 26A. In some embodiments,if the frequency switching does not occur at zero crossings, artifactsmay be induced in the electrograms, thereby degrading the quality of theelectrograms. In some embodiments, impedance measurements (for example,bipolar impedance measurements) are obtained at multiple frequenciessimultaneously. In other embodiments, impedance measurements areobtained at multiple frequencies sequentially.

In another embodiment, contact sensing or determination is performed byobtaining resistance or impedance measurements across a full range offrequencies from an f_(min) to an f_(max) (for example, 5 kHz to 1 MHz,10 kHz to 100 kHz, 10 kHz to 1 MHz). In such embodiments, the variationin the frequency response, or the impedance measurements over the rangeof frequencies, is indicative of whether the electrode portion 30A is incontact with tissue (for example, cardiac tissue) or not.

The impedance measurements may be applied to a model. For example, afrequency response function r(f) may be created and fit to a polynomialor other fitting function. The function may take the form, for example,of:r(f)=a·f ³ +b·f ² +c·f+dwhere a, b, c and d are the terms for the polynomial function that matchthe response of r(f) to measured data. Thresholds may then be set on thepolynomial terms to determine whether or not the electrode is in contactwith tissue. For example, a large d term may indicate a large impedanceindicative of tissue contact. Similarly, a large c term may indicate alarge slope in the impedance which is also indicative of tissue contact.The higher-order terms may be utilized to reveal other subtledifferences in the impedance response that indicate tissue contact.

In some embodiments, a circuit model such as that shown in FIG. 26B isused to determine the frequency response function r(f). The model maycomprise resistors and capacitors that predict the response of tissueand the tissue to electrode interfaces. In this approach, the R and Cvalues may be determined that best fit the measured data and thresholdsmay be utilized based on the R and C values to determine whether or notthe electrode is in contact with tissue. For example a small value ofcapacitance (C2) may indicate a condition of tissue contact, while alarge value may indicate no contact. Other circuit configurations arealso possible to model the behavior of the electrode impedance asdesired and/or required.

In some embodiments, the contact sensing or contact determinationassessments are performed prior to initiation of ablative energydelivery and not performed during energy delivery. In this case,switching may be utilized to separate the contact impedance measurementcircuitry from the ablative energy, as shown in FIG. 26C. In thisimplementation, a switch SW1 is opened to disconnect the split-tipcapacitor (C_(ST)) and allow measurement of impedance in the higherfrequency ranges where C_(ST) might present a short circuit (or lowimpedance in parallel with the measurement). At the same time, switchesSW2 and SW3 are set to connect to the impedance measurement circuitry,or contact sensing subsystem. As shown in FIG. 26C, the impedancemeasurement circuit, or contact sensing subsystem, is the same as thatshown in FIG. 25D. When ablations are to be performed, SW2 and SW3connect the tip electrodes to the ablative energy source (for example,RF generator labeled as RF in FIG. 26C) and disconnect the impedancemeasurement circuit. SW1 is also switched in order to connect the splittip capacitor C_(ST), thereby allowing the pair of electrodes to beelectrically connected via a low impedance path. In one embodiment, thesplit-tip capacitor C_(ST) comprises a 100 nF capacitor that introducesa series impedance lower than about 4Ω at 460 kHz, which, according tosome arrangements, is a target frequency for radiofrequency ablation. AsFIG. 26C also shows, the ablation current path is from both electrodesto a common ground pad. The impedance measurement path is between thetwo electrodes, although other current paths for the impedancemeasurement are also possible. In one embodiment, the switch is a relaysuch as an electromechanical relay. In other embodiments, other types ofswitches (for example, solid-state, MEMS, etc.) are utilized.

In some embodiments, the contact sensing or contact determinationassessments described above may be performed while ablative energy orpower (for example, ablative radiofrequency energy or power) is beingdelivered because the frequencies being used for contact sensing areoutside of the range (either above or below, or both) of the ablationfrequency(ies).

FIG. 27 schematically illustrates a system 4600 comprising ahigh-resolution, combination electrode, or split-tip, electrodecatheter, the system being configured to perform ablation procedures andcontact sensing or determination procedures simultaneously. The highresolution (e.g., split-tip) electrode assembly 4615 may comprise twoelectrodes or two electrode members or portions 4630A, 4630B separatedby a gap. A separator is positioned within the gap G, between theelectrodes or electrode portions 4630A, 4630B. The split-tip electrodeassembly 4615 may comprise any of the features of the split-tipelectrode assemblies described above in connection with FIG. 2 andand/or as otherwise disclosed herein. An energy delivery module (notshown, such as energy delivery module 40 of FIG. 1) or other signalsource 4605 may be configured to generate, deliver and/or apply signalsin an ablative range (for example, radiofrequency energy 200 kHz-800kHz, and nominally 460 kHz) while a contact sensing subsystem 4650 (suchas the contact sensing subsystem shown in FIG. 25D) delivers low-powersignal(s) 4607 (such as excitation signals) in a different frequencyrange (for example, between 5 kHz and 1000 kHz) to be used to performthe contact sensing or determination assessments to a split-tipelectrode assembly 4615. The low-power signal(s) 4607 may comprise amulti-tone signal or waveform or separate signals having differentfrequencies. The contact sensing subsystem 4650 may comprise theelements shown in FIG. 25D, as well as notch filter circuits to blockthe ablation frequency (for example, a 460 kHz notch filter if a 460 kHzablation frequency is used). In this configuration, a filter 4684 isutilized to separate the contact sensing frequencies and the ablationfrequency(ies).

The filter 4684 may comprise, for example, an LC circuit element, or oneor more capacitors without an inductor. The elements and values of thecomponents of the filter 4684 may be selected to center the minimumimpedance at the center frequency of the ablative frequencies deliveredby the energy delivery module to effect ablation of targeted tissue. Insome embodiments, the filtering element 4684 comprises a singlecapacitor that electrically couples the two electrodes or electrodeportions 4630A, 4630B when radiofrequency current is applied to thesystem. In one embodiment, the capacitor comprises a 100 nF capacitorthat introduces a series impedance lower than about 4Ω at 460 kHz,which, according to some arrangements, is a target frequency forablation (for example, RF ablation). However, in other embodiments, thecapacitance of the capacitor(s) or other band-pass filtering elementsthat are incorporated into the system can be greater or less than 100nF, for example, 5 nF to 300 nF, according to the operating ablationfrequency, as desired or required. In this case, the contact sensingimpedance frequencies would all be below the ablation frequency range;however, in other implementations, at least some of the contact sensingimpedance frequencies are within or above the ablation frequency range.

FIG. 28 illustrates a plot of impedance of an LC circuit elementcomprising the filter 4684, for example. As shown, the minimum impedanceis centered at the center frequency of the ablative RF frequencies (460kHz as one example) and the impedance is high at the frequencies in theEGM spectrum so as not to affect EGM signals or the contact sensingmeasurements. Additionally, the contact impedance measurements areperformed at frequencies that exist above and/or below the RF frequency(and above the EGM spectrum). For example, two frequencies f₁ and f₂ maybe utilized where f₁=20 kHz and f₂=800 kHz. At these frequencies, the LCcircuit would have a large impedance in parallel with the electrodes,thereby allowing the impedance to be measured. In one embodiment, theinductor L has an inductance value of 240 μH and the capacitor C has acapacitance value of 5 nF. However, in other embodiments, the inductor Lcan range from 30 μH to 1000 μH (for example, 30 to 200 μH, 200 to 300μH, 250 to 500 μH, 300 to 600 μH, 400 to 800 μH, 500 to 1000 μH, oroverlapping ranges thereof) and the capacitor C can range from 0.12 nFto 3.3 μF (for example, 0.12 to 0.90 nF, 0.50 to 1.50 nF, 1 nF to 3 nF,3 nF to 10 nF, 5 nF to 100 nF, 100 nF to 1 μF, 500 nF to 2 μF, 1 μF to3.3 μF, or overlapping ranges thereof). In various embodiments, f₁ isbetween 10 kHz and 100 kHz and f₂ is between 400 kHz and 1000 kHz.

In accordance with several embodiments, the same hardware andimplementation as used for contact sensing may be used to determinetissue type (for example, viable tissue vs. ablated tissue), so as toconfirm whether ablation has been successful or not. FIG. 29 is a plotillustrating resistance, or impedance magnitude, values for ablatedtissue, viable tissue and blood across a range of frequencies. As can beseen, the resistance of ablated tissue starts at a high resistance value(200Ω) and remains substantially flat or stable, decreasing slightlyover the range of frequencies. The resistance of blood starts at a lowerresistance (125Ω) and also remains substantially flat or stable,decreasing slightly over the range of frequencies. The resistance ofviable tissue, however, starts at a high resistance value (250Ω) andsignificantly decreases across the range of frequencies, roughly formingan “s-shaped” curve. The reason for the different resistance responsesbetween ablated and viable tissue is due, at least partially, to thefact that the viable cells (for example, cardiac cells) are surroundedby a membrane that acts as a high-pass capacitor, blocking low-frequencysignals and allowing the higher-frequency signals to pass, whereas thecells of the ablated tissue no longer have such membranes as a result ofbeing ablated. The reason for the substantially flat response for bloodresistance is that most of the blood is comprised of plasma, which ismore or less just electrolytes having low impedance. The red blood cellsdo provide some variance, because they have similar membranes acting ascapacitors as the viable cardiac cells. However, because the red bloodcells constitute such a small percentage of the blood composition, theeffect of the red blood cells is not substantial.

Similar to the contact sensing assessments described above, resistance,or impedance magnitude, values may be obtained at two or morefrequencies (for example, 20 kHz and 800 kHz) and the values may becompared to each other to determine a ratio. In some embodiments, if theratio of the impedance magnitude value at the higher frequency f₂ to theimpedance magnitude value at the lower frequency f₁ is less than athreshold, then the processing device (for example, processing device4624, which may execute a tissue type determination module stored inmemory) determines that the contacted tissue is viable tissue and if theratio of the impedance magnitude value at the higher frequency f₂ to theimpedance magnitude value at the lower frequency f₁ is greater than athreshold, then the processing device 4624 determines that the contactedtissue is ablated tissue. In various embodiments, the predeterminedthreshold has a value between 0.5 and 0.8 (for example, 0.50, 0.55,0.60, 0.65, 0.70, 0.75, 0.80).

In some embodiments, a combination of impedance magnitude differencesand differences in the ratio of impedance magnitudes at frequencies f₂and f₁ are utilized to determine both contact state (for example,contact vs. in blood) as well as tissue type (for example, viable tissuevs. ablated tissue). In some embodiments, contact state and tissue typedeterminations are not performed during energy delivery or othertreatment procedures. In other embodiments, contact state and/or tissuetype determinations are performed during energy delivery or othertreatment procedures using filters and/or other signal processingtechniques and mechanisms to separate out the different frequencysignals.

In addition to the impedance magnitude, the same hardware andimplementation used for contact sensing (for example, contact sensingsubsystem 50, 4650) may be utilized to compute the phase of theimpedance (for example, complex impedance) across electrode portions. Inone embodiment, the phase of the impedance may be added to algorithmsfor determining different contact states (for example, contact vs. inblood) as well as different tissue states (for example, viable tissuevs. ablated tissue). FIG. 30 shows an example of the phase of theimpedance across electrode portions versus frequency for viable tissue,ablated tissue and blood. The phase tends to be larger (closer to 0degrees) for blood and smaller for viable (unablated) tissue. Forablated tissue the phase may be in between blood and viable tissue. Inone embodiment, a negative phase shift at a single frequency indicatescontact with tissue (either viable or ablated). A larger negative phaseshift may indicate contact with viable tissue. In one embodiment, aphase of less than −10 degrees at 800 kHz indicates contact with tissue(either viable or ablated). In one embodiment, a phase of less than−20.5 degrees at 800 kHz indicates contact with viable tissue. In otherembodiments, the phase at other frequencies or combinations offrequencies are utilized to determine contact state and tissue type. Insome embodiments, the impedance magnitude and phase are utilizedtogether as vector quantities, and differences in the vectors fordifferent frequencies are utilized to determine contact state and tissuetype.

In some embodiments, a combination of impedance magnitude differences,differences in the ratio of impedance magnitude values at frequencies f₂and f₁, and differences in the phase of the impedance are utilizedtogether to determine both contact state (for example, contact vs. inblood) as well as tissue type (for example, viable tissue vs. ablatedtissue). In one embodiment, the determination process 5000 illustratedin FIG. 31 is utilized to determine both contact state as well as tissuetype. In this embodiment, an impedance magnitude threshold of 150Ω at 20kHz is utilized to delineate between no contact and tissue contact (witha larger value indicating contact) at block 5005. Once contact isdetermined at block 5005, the ratio of the impedance magnitude at f₂=800kHz and f₁=20 kHz is computed at block 5010, with a value of less than0.6 indicating contact with unablated, or viable, tissue. If theaforementioned ratio is greater than 0.6, then the impedance phase at800 kHz is utilized at block 5015, and an (absolute) value greater than20.5 degrees indicates contact with ablated tissue. An (absolute) valueof less than 20.5 degrees indicates contact with unablated, or viable,tissue.

In some embodiments, the contact sensing subsystem 50 or system 10 (forexample, a processing device thereof) analyzes the time-domain responseto the waveform described in FIG. 25B, or to an equivalent waveform. Inaccordance with several embodiments, contact sensing or tissue typedeterminations are based on processing the response to a signal appliedto a pair of electrodes or electrode portions (for example electrodepair 4630A, 4630B), the signal either including multiple frequencies orseveral frequencies applied sequentially. In some embodiments,processing device 4624 may process the response in time domain orfrequency domain. For example, given that blood is mostly resistive,with little capacitive characteristics, it is expected that time-domainfeatures such as rise or fall times, lag or lead times, or delaysbetween applied signal 4402 (for example, I in FIG. 25D) and processedresponse 4404 (for example, V2 in FIG. 25D) will exhibit low values.Conversely, if the electrode pair 4630A, 4630B of FIG. 27 is in contactwith tissue, given that tissue exhibits increased capacitivecharacteristics, it is expected that time-domain features such as riseor fall times, lag or lead times, or delays between applied signal 4402(for example, I in FIG. 25D) and processed response 4404 (for example,V2 in FIG. 25D) will exhibit higher values. An algorithm that processesparameters such as, but not limited to, rise or fall times, lag or leadtimes, or delays between applied signal 4402 and processed response 4404may indicate or declare contact with tissue when the parameters exceed athreshold, or, conversely, it may indicate or declare no contact withtissue when the parameters have values below a threshold. For example,assuming the signal 4402 is represented by a sinusoidal current of 800kHz frequency, the algorithm could declare contact with tissue if theresponse 4404 lags by more than 0.035 μs. Conversely, the algorithmcould declare lack of tissue contact if the response 4404 lags by lessthan 0.035 μs. Similarly, if the frequency of signal 4402 were 400 kHz,the algorithm may decide:

-   -   no tissue contact, when the lag time is less than 0.07 μs;    -   contact with ablated tissue, when the lag time is between 0.07        μs and 0.13 μs;    -   contact with viable or unablated tissue, when the lag time is        greater than 0.13 μs.        The decision thresholds or criteria depend on the waveform of        signal 4402. Thresholds or decision criteria for other types of        waveforms may also be derived or determined.

In some embodiments, multiple inputs may be combined by a contactsensing or contact indication module or subsystem executable by aprocessor (for example, processor of the contact sensing subsystems 50,4650) to create a contact function that may be used to provide anindication of contact vs. no contact, an indication of the amount ofcontact (for example, qualitative or quantitative indication of thelevel of contact, contact state or contact force), and/or an indicationof tissue type (for example, ablated vs. viable (non-ablated) tissue).For example, a combination of (i) impedance magnitude at a firstfrequency f₁, (ii) the ratio of impedance magnitudes at two frequenciesf₂ and f₁ (defined as the slope) or the delta, or change, in impedancemagnitudes at the two frequencies, and/or (iii) the phase of the compleximpedance at the second frequency f₂ are utilized together to create acontact function that is indicative of contact state (for example,tissue contact vs. in blood). Alternatively, instead of slope, aderivative of impedance with respect to frequency may be used.

In one embodiment, a minimum threshold |Z|_(min) is defined for theimpedance magnitude at f₁, and a maximum threshold |Z|_(max) is definedfor the impedance at f₁. The impedance magnitude measured by the contactsensing subsystem 50, 650 at f₁ can be normalized such that theimpedance magnitude is 0 if the measured result is equal to |Z|_(min) orbelow, and the impedance magnitude is 1 if the measured result is equalto |Z|_(max) or above. Results in-between |Z|_(min) and |Z|max may belinearly mapped to a value between 0 and 1. Similarly, a minimumthreshold S_(min) and a maximum threshold S_(max) may be defined for theslope (ratio of impedance magnitude between f₂ and f₁). If a derivativeof impedance with respect to frequency is used, then similar minimum andmaximum thresholds may be defined. The slope measured by the contactsensing subsystem 50 may be normalized such that the slope is 0 if themeasured result is equal to or above S_(min) and the slope is 1 if themeasured result is equal to or below S_(max). Results in between S_(min)and S_(max) may be linearly mapped to a value between 0 and 1. A minimumthreshold P_(min) and a maximum threshold P_(max) may also be definedfor the phase of the complex impedance at f₂. The phase measured by thecontact sensing subsystem 50 at f₂ may be normalized such that the phaseis 0 if the measured result is equal to or greater than P_(min) and 1 ifthe measured result is equal to or less than P_(max).

In accordance with several embodiments, the resulting three normalizedterms for magnitude, slope and phase are combined utilizing a weightingfactor for each. The sum of the weighting factors may be equal to 1 suchthat the resulting addition of the three terms is a contact indicatorthat goes from a zero to 1 scale. The weighted contact function (CF) canthus be described by the below equation:

${CF} = {{{WF}\; 1\frac{{Z}_{f\; 1} - {Z}_{\min}}{{Z}_{\max} - {Z}_{\min}}} + {{WF}\; 2\frac{S - S_{\min}}{S_{\max} - S_{\min}}} + {{WF}\; 3\frac{P_{f\; 2} - P_{\min}}{P_{\max} - P_{\min}}}}$

where |Z|_(f1) is the measured impedance magnitude at a first frequencyf₁, clipped to a minimum value of |Z|_(min) and a maximum value of|Z|_(max) as described above; S is the ratio of the impedance magnitudeat a second frequency f₂ to the magnitude at f₁, clipped to a minimumvalue of S_(min) and a maximum value of S_(max) as described above; andP_(f2) is the phase of the impedance at frequency f₂, clipped to aminimum value of P_(min) and a maximum value of P_(max) as describedabove. The weighting factors WF1, WF2 and WF3 may be applied to themagnitude, slope and phase measurements, respectively. As previouslystated, the weighting factors WF1+WF2+WF3 may sum to 1, such that theoutput of the contact function always provides a value ranging from 0to 1. Alternatively, values greater than 1 may be allowed to facilitategeneration of alerts to a user about circumstances when moretissue-electrode contact may become unsafe for patients. Such alerts maybe helpful in preventing application of unsafe levels of contact force.For example, CF values in the range of 1 to 1.25 may be flagged as a“contact alert” and may cause the contact sensing subsystem to generatean alert for display or other output to a user. The alert may be visual,tactile, and/or audible. The weighting factors may vary based oncatheter design, connection cables, physical patient parameters, and/orthe like. The weighting factors may be stored in memory and may beadjusted or modified (for example, offset) depending on variousparameters. In some embodiments, the weighting factors may be adjustedbased on initial impedance measurements and/or patient parametermeasurements.

The contact function described above can be optimized (for example,enhanced or improved) to provide a reliable indicator of the amount ofcontact with tissue (for example, cardiac tissue, such as atrial tissueor ventricular tissue). The optimization may be achieved by definingminimum thresholds Z_(min), S_(min) and P_(min) that correspond with noto minimal tissue contact, as well as thresholds Z_(max), S_(max) andP_(max) that correspond with maximal tissue contact. Weighting terms mayalso be optimized (for example, enhanced or improved) for robustresponsiveness to contact. In some embodiments, windowed averaging orother smoothing techniques may be applied to the contact function toreduce measurement noise.

As one example, at a frequency f₁=46 kHz and f₂=800 kHz, the valuesZ_(min)=115 ohms, Z_(max)=175 ohms, S_(min)=0.9, S_(max)=0.8,P_(min)=−5.1 degrees, P_(max)=−9 degrees, WF1=0.75, WF2=0.15, andWF3=0.1 are desirable (for example, optimal) for representing the amountof tissue contact (for example, for cardiac tissue of the atria orventricles). In other embodiments, Z_(min) may range from 90 ohms to 140ohms (for example, 90 ohms to 100 ohms, 95 ohms to 115 ohms, 100 ohms to120 ohms, 110 ohms to 130 ohms, 115 ohms to 130 ohms, 130 ohms to 140ohms, overlapping ranges thereof, or any value between 90 ohms and 140ohms), Z_(max) may range from 150 ohms up to 320 ohms (for example, 150ohms to 180 ohms, 160 ohms to 195 ohms, 180 ohms to 240 ohms, 200 ohmsto 250 ohms, 225 ohms to 260 ohms, 240 ohms to 300 ohms, 250 ohms to 280ohms, 270 ohms to 320 ohms, overlapping ranges thereof, or any valuebetween 150 ohms and 320 ohms), S_(min) may range from 0.95 to 0.80 (forexample, 0.95 to 0.90, 0.90 to 0.85, 0.85 to 0.80, overlapping rangesthereof, or any value between 0.95 and 0.80), S_(max) may range from0.85 to 0.45 (for example, 0.85 to 0.75, 0.80 to 0.70, 0.75 to 0.65,0.70 to 0.60, 0.65 to 0.55, 0.60 to 0.50, 0.55 to 0.45, overlappingranges thereof, or any value between 0.85 and 0.45), P_(min) may rangefrom 0 to −10 degrees (for example, 0, −1, −2, −3, −4, −5, −6, −7, −8,−9, −10 or any combinations of ranges between, such as 0 to −5, −2 to−6, −4 to −8, −5 to −10), and P_(max) may range from −5 to −25 degrees(for example, −5 to −10, −7.5 to −15, −10 to −20, −15 to −25,overlapping ranges thereof or any value between −5 and −25 degrees). Theweighting factors WF1, WF2 and WF3 may cover the range from 0 to 1. Insome embodiments, values above or below the ranges provided may be usedas desired and/or required. Appropriate values for these parameters maybe dependent on the electrode geometry and frequencies f₁ and f₂ usedfor the measurements. Changes in the electrode geometry, physicalpatient parameters, connection cables, and frequencies may requiredifferent ranges for the above values.

In some embodiments, a contact function, or contact criterion, can bedetermined based, at least in part, on an if-then case conditionalcriterion. One example if-then case criterion is reproduced here:

CC=IF(|Z_(MAG)|>Z_(THR1), Best, IF(AND(Z_(THR1)>|Z_(MAG)|,|Z_(MAG)|>Z_(THR2)), Good, IF(AND(Z_(THR2)>|Z_(MAG)|,|Z_(MAG)|≥Z_(THR3)), Medium, IF(AND(Z_(THR3)>|Z_(MAG),|Z_(MAG)|≥Z_(THR4)), Low, No_Contact))))+IF(|Z_(MAG)|>Z_(THR1), 0,IF(AND(SLOPE ≤S_(THR1)), Good, IF(AND(S_(THR1)<SLOPE, SLOPE ≤S_(THR2)),Medium, IF(AND(S_(THR2)<SLOPE, SLOPE ≤S_(THR3)), Low,No_Contact))))+IF(|Z_(MAG)|>Z_(THR1), 0, IF(AND(PHASE ≤P_(THR1)), Good,IF(AND(P_(THR1)<PHASE, PHASE ≤P_(THR2)), Medium, IF(AND(P_(THR2)<PHASE,PHASE ≤P_(THR3)), Low, No_Contact))))

FIG. 32 illustrates an embodiment of a contact criterion process 5100corresponding to the above if-then case conditional criterion. Thecontact criterion process 5100 may be executed by a processor uponexecution of instructions stored in memory or a non-transitorycomputer-readable storage medium. At decision block 5105, a measured orcalculated impedance magnitude value (for example, based on directimpedance measurements or based on voltage and/or current measurementsobtained by a combination electrode assembly comprising two electrodeportions) is compared to a predetermined threshold impedance. If themeasured or calculated impedance magnitude value |Z_(MAG)| is greaterthan a first threshold Z_(THR1) (for example, 350Ω), then the ContactCriterion (CC) is assigned a “best” or highest value. If, however, themeasured or calculated impedance magnitude value |Z_(MAG)| is less thanthe threshold Z_(THR1), then the process 5100 proceeds to block 5110,where individual subvalues for impedance magnitude, slope and phase aredetermined. At block 5115, the individual subvalues are combined (forexample summed) into an overall value indicative of contact state. Insome embodiments, the combination is a sum of a weighted combination, asdescribed above.

The process 5100 may optionally generate output at block 5120. Forexample, if at decision block 5105, the measured or calculated impedancemagnitude value |Z_(MAG)| is greater than the first threshold Z_(THR1),the process can generate an alert to a user that further manipulation ofthe catheter or other medical instrument may not further improve tissuecontact, but may instead compromise patient safety. For example, if theuser pushes too hard on the catheter or other medical instrument, theadditional pressure may achieve little improvement in tissue contact butmay increase the risk of tissue perforation (for example, heart wallperforation). The output may comprise a qualitative or quantitativeoutput as described in further detail herein (for example in connectionwith FIG. 33).

FIG. 32A illustrates an embodiment of the individual subvalue subprocess5110 of process 5100 performed when the measured or calculated impedancemagnitude value |Z_(MAG)| is less than the first threshold Z_(THR1). TheContact Criterion (CC) overall value may be calculated by bracketing theimpedance magnitude (|Z_(MAG)|), the slope (S) and the phase (P) intointervals corresponding to good, medium, low and no contact levels.Subvalues corresponding to either good, medium, low or not contact aredetermined for each of the impedance magnitude, slope and phasecomponents depending on comparisons to various predetermined thresholdvalues. The subvalues may be combined to determine an overall contactstate value. In the example case conditional criterion above, the CC isa sum of the individual values received by each of the three parameters(|Z_(MAG)|, S, P) according to their corresponding level of contact (forexample, good, medium, low or no contact). For example, if Good=3,Medium=2, Low=1 and No_Contact=0 then the overall CC could be between0-2 for no or low contact, between 3-4 for poor contact, between 5-6 formedium contact and 7-9 for good contact. In one embodiment, when|Z_(MAG)| exceeds the first threshold Z_(THR1), then CC=10, as anindication that a “best,” or “optimal” level of tissue contact wasachieved.

In some embodiments, more than two frequencies are used (for example,three or four frequencies) for tissue contact or tissue type detection.Although the computations described above were presented using impedancemagnitude, slope and phase, other characteristics of the compleximpedance may be used in other embodiments. For example, analyses of thereal and imaginary components of impedance may be used. Analyses ofadmittance parameters or scattering parameters may also be used. In someembodiments, direct analyses of the voltages and currents described inFIGS. 25A-27 (for example, processing of voltage or current magnitudes,frequency changes or relative phase) may be used. Analyses of voltagesor currents may be performed in time domain or frequency domain.Impedance measurements, or values, may be calculated based on voltageand current measurements or may be directly measured. For example, phasemeasurements may comprise a difference in phase between measured voltageand measured current or may be actual impedance phase measurements.

In some embodiments, the contact indicator or contact function isassociated with output via an input/output interface or device. Theoutput may be presented for display on a graphical user interface ordisplay device communicatively coupled to the contact sensing subsystem50 (FIG. 1). The output may be qualitative (for example, comparativelevel of contact as represented by a color, scale or gauge) and/orquantitative (for example, represented by graphs, scrolling waveforms ornumerical values) as shown in FIG. 33.

FIG. 33 illustrates an embodiment of a screen display 5200 of agraphical user interface of a display device communicatively coupled tothe contact sensing subsystem 50 (FIG. 1). The screen display 5200includes a graph or waveform 5210 illustrating impedance magnitude atfrequency f₁ over time, as well as a box 5211 indicating the real-timenumerical value of the impedance magnitude. The screen display 5100 alsoincludes a graph or waveform 5220 of slope (from f₂ to f₁) over time, aswell as a box 5221 indicating the real-time numerical value of theslope. The screen display 5200 further includes a graph or waveform 5230illustrating phase at frequency f₂ over time, as well as a box 5231indicating the real-time numerical value of the phase. The threemeasurements (magnitude, slope and phase) are combined into a contactfunction as described above and may be represented as a contact functionor indicator over time, as displayed on graph or waveform 5240. Thereal-time or instantaneous numerical value of the contact function mayalso be displayed (Box 5241).

In some embodiments, as shown in FIG. 33, the contact function orindicator may be represented as a virtual gauge 5250 that provides aqualitative assessment (either alone or in addition to a quantitativeassessment) of contact state or level of contact in a manner that iseasily discernable by a clinician. The gauge 5250 may be segmented into,for example, four segments, or regions, that represent differentclassifications or characterizations of contact quality or contactstate. For example, a first segment (for example, from contact functionvalues of 0 to 0.25) may be red in color and represent no contact, asecond segment (for example, from contact function values of 0.25 to0.5) may be orange in color and represent “light” contact, a thirdsegment (for example, from contact function values of 0.5 to 0.75) maybe yellow in color and represent “medium” or “moderate” contact, and afourth segment (for example, from contact function values of 0.75 to 1)may be green in color and represent “good”, or “firm”, contact. In otherembodiments, fewer than four segments or more than four segments may beused (for example, two segments, three segments, five segments, sixsegments). In one embodiment, three segments are provided, one segmentfor no contact or poor contact, one segment for moderate contact and onesegment for good, or firm, contact. The segments may be divided equallyor otherwise as desired and/or required. Other colors, patterns,graduations and/or other visual indicators may be used as desired.Additionally, a “contact alert” color or gauge graduation may beprovided to alert the user about engaging the catheter or other medicalinstrument with too much force (for example, contact function valuesgreater than 1). The gauge 5250 may include a pointer member that isused to indicate the real-time or instantaneous value of the contactfunction on the gauge 5250.

In some embodiments, a qualitative indicator 5260 indicates whether ornot contact is sufficient to begin a treatment (for example, ablation)procedure, the level of contact, tissue type, and/or whether contact isgreater than desired for safety. The qualitative indicator 5260 mayprovide a binary indication (for example, sufficient contact vs.insufficient contact, contact or no contact, ablated tissue or viabletissue) or a multi-level qualitative indication, such as that providedby the gauge 5250. In one embodiment, the qualitative indicator 5260displays the color on the gauge 5250 corresponding to the currentcontact function value. Other types of indicators, such as horizontal orvertical bars, other meters, beacons, color-shifting indicators or othertypes of indicators may also be utilized with the contact function toconvey contact quality to the user. Indicators may include one or morelight-emitting diodes (LEDs) adapted to be activated upon contact (or asufficient level of contact) or loss of contact. The LEDs may bedifferent colors, with each color representing a different level ofcontact (for example, red for no contact, orange for poor contact,yellow for medium contact and green for good contact). The LED(s) may bepositioned on the catheter handle, on a display or patient monitor, orany other separate device communicatively coupled to the system.

In one embodiment involving delivery of radiofrequency energy using aradiofrequency ablation catheter having a plurality oftemperature-measurement devices (such as the ablation catheters andtemperature-measurement devices described herein), the criterion fordetecting a loss of tissue contact during delivery of radiofrequencyenergy may be implemented as:ΔT _(i) /Δt<−Threshold1  (Condition 1)orΔT _(comp) /ΔP<Threshold2  (Condition 2)where ΔT_(i) is the change in the temperature of any of the plurality oftemperature-measurement devices (for example, sensors, thermocouples,thermistors) positioned along the catheter or other medical instrument;Δt is the interval of time over which the temperature change ismeasured; ΔT_(comp) is the change in the maximum of the temperatures ofthe temperature-measurement devices and ΔP is the change in appliedpower.

Condition 1 may signal that the temperature measurements obtained by thetemperature-measurement devices have dropped rapidly in a short periodof time, which may be indicative of a loss of contact or an insufficientor inadequate level of contact. For example, if ΔT_(i) is −10 degreesCelsius over a Δt of 1 second and Threshold1 is −5 degreesCelsius/second, then the contact loss condition is met (because −10degrees Celsius/second<−5 degrees Celsius/second).

Condition 2 may signal that the temperature of thetemperature-measurement devices is not increasing even though sufficientpower is being applied, which may be indicative of a loss of contact oran insufficient or inadequate level of contact. For example, ifΔT_(comp)=5 degrees Celsius and ΔP=30 Watts and if Threshold2 is 1degree Celsius/Watt, then the contact loss condition is met (because 5degrees Celsius/30 Watts <1 degree Celsius/Watt).

In accordance with several embodiments, systems and methods forde-embedding, removing, or compensating for the effects caused byvariations in cables, generators, wires and/or any other component of anablation system (and/or components operatively coupled to an ablationsystem) or by the presence or absence of a catheter interface unit orother hardware component in an energy delivery and mapping system areprovided. In some embodiments, the systems and methods disclosed hereinadvantageously result in contact indication values that are based onnetwork parameter values (for example, impedance values) that moreclosely represent the actual network parameter value (for example,impedance) across the electrodes of the high resolution electrodeassembly. Accordingly, as a result of the compensation or calibrationsystems and methods described herein, a clinician may be more confidentthat the contact indication values are accurate and are not affected byvariations in the hardware or equipment being used in or connected tothe system or network parameter circuit. In some arrangements, thenetwork parameter values (for example, impedance measurements) obtainedby the system using the compensation or calibration embodimentsdisclosed herein can be within ±10% (for example, within ±10%, 9%, 8%,7%, 6%, 5%, 4%, 3%, 2%) of the actual network parameter values (forexample, impedance values) across the electrode members of thecombination electrode assembly. For example, the impedance magnitude,the impedance slope (ratio of impedance magnitudes at two frequencies)and phase of the impedance may each individually be measured to within+/−10% or better using this approach. As a result, the contact functionor contact indicator can advantageously provide an accuraterepresentation of tissue contact, with an accuracy of +/−10% or greater.

FIG. 34A illustrates a schematic block diagram of an embodiment of anetwork parameter measurement circuit 5400 (for example, tissue contactimpedance measurement circuit). The network parameter measurementcircuit 5400 includes a contact sensing signal source 5405, a load 5410between two electrodes D1, D2 of a high-resolution electrode assembly ata distal end portion of an ablation catheter, and a chain of multipletwo-port networks representative of a generator 5415, catheter interfaceunit cables 5420A, 5420B, a catheter interface unit 5425, a generatorcable 5430 and catheter wires 5435. Because in some arrangements thenetwork parameter values (for example, scattering parameter orelectrical measurement such as voltage, current or impedancemeasurements) are obtained at the beginning of the chain at the level ofthe generator 5415, the measured network parameter values (for example,impedance values obtained directly or from voltage and/or currentvalues) may differ significantly from the actual network parametervalues (for example, impedance values) between the two spaced-apartelectrode members D1, D2 due to effects of the components of the networkparameter circuit between the signal source 5405 and the electrodemembers D1, D2. The impedance values may comprise impedance magnitude,slope between impedance magnitude at different frequencies, and/orimpedance phase values. For example, detected impedance magnitude at afrequency f₁ can be as much as ±25% different than the actual impedancemagnitude at a frequency f₁. Similarly, a detected slope (ratio ofimpedance magnitudes at frequencies f₂ and f₁) can be as much as ±50%different than the actual slope. Additionally, the detected phase may beas much as ±−30 degrees different than the actual phase. As a result ofthese combined inaccuracies, a contact function (CF) or contactindication values may be as much as −100% or +150% different than theintended contact function or contact indication values, therebyrendering the contact function ineffective in determining tissuecontact. In accordance with several embodiments, the compensation orcalibration embodiments disclosed herein can advantageously improve theaccuracy of the contact function or contact indication values.

The network parameters of each of the multi-port (for example, two-port)networks in the network parameter measurement circuit 5400 can beobtained (for example, measured) and utilized to convert the measurednetwork parameter value (for example, scattering parameter or electricalparameter such as impedance) to a corrected (actual) value (for example,impedance value). In some embodiments, a two-port network analyzer isused to directly measure the scattering parameters (S-parameters) at theinput and output of each of the two-port networks. In other embodiments,multiple components of the network parameter measurement circuit 5400can be combined into groups of components and measured together. Thenetwork parameters of the individual components or groups of componentscan be combined to determine an aggregate effect of the chain oftwo-port networks on the network parameter value(s). In someimplementations, the scattering parameters of at least some of thecomponents may be hard-coded into a software program (for example, usingan average value based on a few measurement samples) so as to reduce thenumber of measurements to be taken or obtained.

According to one implementation, S-parameter matrices for each of thetwo-port networks or groups of two-port networks can be transformed toan overall transmission matrix. The overall transmission matrix may thenbe transformed back into S-parameters (or some other parameters) togenerate an S-parameter (or another type of) matrix for the totalnetwork. The S-parameters from the total S-parameter matrix can then beused to de-embed, calibrate or compensate for the S-parameters from themeasured input reflection coefficient to result in a corrected (actual)reflection coefficient. The actual reflection coefficient may then beconverted into a corrected impedance value that is more closelyindicative of the actual impedance between the two electrode portionsD1, D2 of a high-resolution electrode assembly. In several embodiments,the corrected impedance values are used as the inputs for the ContactFunction (CF) or other contact indication or level of contact assessmentalgorithm or function, as described above. For example, the correctedimpedance values can be used to determine the Z, S and P values in theweighted contact function (CF) described above.

The effects of the hardware components of the network parametermeasurement circuit (for example, impedance measurement circuit) 5400can be compensated for, de-embedded from, or calibrated so as to reduceor remove the effects of the hardware components or differences in thehardware components of a particular system (for example, impedancemeasurement circuit) setup prior to first use; however, the componentsof the network parameter circuit may differ across different proceduresas different hardware components (for example, generators, cables,catheters and/or the like) are used or as a catheter interface unit orother hardware component to facilitate electroanatomical mapping isplugged in or removed, thereby resulting in inconsistency if notcompensated for. In some embodiments, the total system S-parametermatrix may only be updated when the connections within the networkparameter measurement circuit 5400 change (for example, when a catheterinterface is plugged in or removed from the electrical path, when acable is switched, etc.).

In some embodiments, instead of requiring a manual de-embedding of theeffects on impedance of certain circuit components when connectionschange (which can be time-consuming and result in increased likelihoodof user error), the network parameters of a subset of the variouscomponents (for example, the generator 5415, the catheter interface unitcables 5420A, 5420B and the catheter interface unit 5425) areautomatically measured to enable the effects of these elements to bede-embedded from the network parameters (for example, scatteringparameters or impedance measurements) or otherwise compensated for orcalibrated. FIG. 34B illustrates an embodiment of a circuit 5450 thatcan be used to automatically de-embed or compensate for the effects ofcertain hardware components in the network parameter circuit 5400. Inone embodiment, the auto-calibration circuit 5450 is positioned at adistal end of the catheter interface unit cable before the generatorcable 5430 and catheter wires 5435. The circuit 5450 may advantageouslyprovide the ability to disconnect the electrode members D1, D2 of thehigh-resolution electrode assembly from the generator cable 5430 andcatheter 5435 and to connect a known load between D1 and D2.

In this embodiment, the auto-calibration circuit 5450 can assume thatthe network parameters of the generator cable 5430 and catheter wire5435 components are known and can be assumed to be constant. However, ifthe generator cable 5430 and/or catheter wires 5435 are determined tovary significantly from part to part, the circuit 5450 could beimplemented at the distal end of the generator cable 5430, in thecatheter tip or at any other location, as desired or required. In someembodiments, the known load of the auto-calibration circuit 5450includes a calibration resistor R_(cal) and a calibration capacitorC_(cal). Switches may be used to connect R_(cal) as the load, C_(cal) asthe load and both R_(cal) and C_(cal) in parallel as the load. Otherelements (such as inductors, combinations of resistors, inductors and/orcapacitors, or shorts or open circuits can be utilized as the knownload). As shown in FIG. 34B, the combined network parameters of thegenerator 5415, catheter interface unit cables 5420A, 5420B and thecatheter interface unit 5425 are represented as a single combinednetwork (Network 1).

In this embodiment, the network parameters (for example S-parameters) ofNetwork 1 are measured directly using the network parameter circuit andan S-parameter matrix is created from the network parameters. Each ofthe elements in the S-parameter matrix is a complex number and isfrequency dependent. The S-parameters may be measured at multipledifferent frequencies (for example, 3 different frequencies in the kHzrange, such as a first frequency from 5-20 kHz a second frequency from25-100 kHz and a third frequency from 500-1000 kHz). In one embodiment,the complex impedance is measured with the resistor R_(cal) connectedand the capacitor C_(cal) disconnected, with the capacitor C_(cal)connected and the resistor R_(cal) disconnected and with both theresistor R_(cal) and the capacitor C_(cal) connected in parallel. Therelationship between the measured complex impedance, the S-parameters ofNetwork 1 and the known load can be expressed as three equations, whichcan then be used to solve for the S-parameters of Network 1. Once theS-parameters are characterized, they can be combined (for example, usinga transmission matrix approach) with the known network parameters of thegenerator cable 5430 and catheter wires 5435 to provide corrected(actual) impedance measurements at the distal end portion of thecatheter (for example, across two spaced-apart electrode portions of acombination electrode assembly).

The automatic calibration techniques and systems described hereinadvantageously allow for increased confidence in the contact indicationvalues regardless of the generator, cables, catheter or other equipmentbeing used and regardless of whether a hardware component to facilitatesimultaneous electroanatomical mapping (for example, a catheterinterface unit) is connected. The various measurements may be performedautomatically upon execution of instructions stored on acomputer-readable storage medium executed by a processor or may beperformed manually.

The automatic calibration systems and methods described herein may alsobe implemented using an equivalent circuit model for one or morehardware components of the system (for example, the generator circuitry,cable and catheter wiring). In such implementations, the equivalentcircuit model comprises one or more resistors, one or more capacitorsand/or one or more inductors that approximate an actual response of theone or more hardware components being represented. As one example, agenerator cable component 5430 can be represented by a transmission-lineequivalent RLC model as shown in FIG. 34C, where the measurement of theimpedance Z_(meas) would be performed at Port 1 with the actual(corrected) impedance Z_(act) desired being at Port 2. In this example,if the impedance measurement circuit is measuring an impedance Z_(meas),the actual impedance measurement Z_(act) can be extracted by usingcircuit analysis techniques. The equation relating the two impedances isgiven by:

$Z_{meas} = {R + \;{j\;\omega\; L} + \frac{Z_{act}}{1 + {j\;\omega\;{C \cdot Z_{act}}}}}$

The actual values for R, L and C may be extracted from network parametermeasurements. For example if we measure the impedance (Z) parameters ofthis network, we can derive the following relationships:

$Z_{11} = {{\frac{V_{1}}{I_{1}}l_{({{I\; 2} = 0})}} = {R + \;{j\;\omega\; L} + \frac{1}{j\;\omega\; C}}}$$Z_{21} = {{\frac{V_{2}}{I_{1}}l_{({{I\; 2} = 0})}} = \frac{1}{j\;\omega\; C}}$Z₁₁ − Z₂₁ = R+ j ω L

where 1 and 2 denote the port numbers of the circuit, and V₁, I₁, V₂ andI₂ represent the voltages and currents at each of the respective ports.The values for R, L and C may also be measured utilizing measurementtools (for example, a multimeter). The equivalent circuit model approachdescribed above is an example of this concept. In other implementations,more complex circuit models may be utilized to represent the variouselements of the system.

In some embodiments, the system comprises one or more of the following:means for tissue modulation (for example, an ablation or other type ofmodulation catheter or delivery device), means for generating energy(for example, a generator or other energy delivery module), means forconnecting the means for generating energy to the means for tissuemodulation (for example, an interface or input/output connector or othercoupling member), means for performing tissue contact sensing and/ortissue type determination, means for displaying output generated by themeans for performing tissue contact sensing and/or tissue typedetermination, means for determining a level of contact with tissue,means for calibrating network parameter measurements in connection withcontact sensing means, etc.

In some embodiments, the system comprises various features that arepresent as single features (as opposed to multiple features). Forexample, in one embodiment, the system includes a single ablationcatheter with a single high-resolution (e.g., split-tip) electrode andone or more temperature sensors (e.g., thermocouples) to help determinethe temperature of tissue at a depth. The system may comprise animpedance transformation network. In some embodiments, the systemincludes a single ablation catheter with a heat shunt network for thetransfer of heat away from the electrode and/or tissue being treated. Insome embodiments, the system includes a single contact sensing subsystemfor determining whether there is and to what extent there is contactbetween the electrode and targeted tissue of a subject. Multiplefeatures or components are provided in alternate embodiments.

In one embodiment, the system comprises one or more of the following:means for tissue modulation (e.g., an ablation or other type ofmodulation catheter or delivery device), means for generating energy(e.g., a generator or other energy delivery module), means forconnecting the means for generating energy to the means for tissuemodulation (e.g., an interface or input/output connector or othercoupling member), etc.

In some embodiments, the system comprises one or more of the following:means for tissue modulation (e.g., an ablation or other type ofmodulation catheter or delivery device), means for measuring tissuetemperature at a depth (e.g., using multiple temperature sensors (e.g.,thermocouples) that are thermally insulated from the electrode and thatare located along two different longitudinal portions of the catheter),means for effectively transferring heat away from the electrode and/orthe tissue being treated (e.g., using heat shunting materials andcomponents) and means for determining whether and to what extent thereis contact between the electrode and adjacent tissue (e.g., usingimpedance measurements obtained from a high-resolution electrode that isalso configured to ablate the tissue).

In some embodiments, the system comprises one or more of the following:an ablation system consists essentially of a catheter, an ablationmember (e.g., a RF electrode, a split-tip electrode, another type ofhigh-resolution electrode, etc.), an irrigation conduit extendingthrough an interior of the catheter to or near the ablation member, atleast one electrical conductor (e.g., wire, cable, etc.) to selectivelyactivate the ablation member and at least one heat transfer member thatplaces at least a portion of the ablation member (e.g., a proximalportion of the ablation member) in thermal communication with theirrigation conduit, at least one heat shunt member configured toeffectively transfer heat away from the electrode and/or tissue beingtreated, a plurality of temperature sensors (e.g., thermocouples)located along two different longitudinal locations of the catheter,wherein the temperature sensors are thermally isolated from theelectrode and configured to detect temperature of tissue at a depth,contact detection subsystem for determining whether and to what extentthere is contact between the electrode and adjacent tissue (e.g., usingimpedance measurements obtained from a high-resolution electrode that isalso configured to ablate the tissue), etc.

In the embodiments disclosed above, a heat transfer member is disclosed.Alternatively, a heat retention sink is used instead of or in additionto the heat transfer member in some embodiments.

According to some embodiments, an ablation system consists essentiallyof a catheter, an ablation member (e.g., a RF electrode, a split-tipelectrode, another type of high-resolution electrode, etc.), anirrigation conduit extending through an interior of the catheter to ornear the ablation member, at least one electrical conductor (e.g., wire,cable, etc.) to selectively activate the ablation member and at leastone heat transfer member that places at least a portion of the ablationmember (e.g., a proximal portion of the ablation member) in thermalcommunication with the irrigation conduit, at least one heat shuntmember configured to effectively transfer heat away from the electrodeand/or tissue being treated and a plurality of temperature sensors(e.g., thermocouples) located along two different longitudinal locationsof the catheter, wherein the temperature sensors are thermally isolatedfrom the electrode and configured to detect temperature of tissue at adepth.

Any methods described herein may be embodied in, and partially or fullyautomated via, software code modules executed by one or more processorsor other computing devices. The methods may be executed on the computingdevices in response to execution of software instructions or otherexecutable code read from a tangible computer readable medium. Atangible computer readable medium is a data storage device that canstore data that is readable by a computer system. Examples of computerreadable mediums include read-only memory, random-access memory, othervolatile or non-volatile memory devices, CD-ROMs, magnetic tape, flashdrives, and optical data storage devices.

In addition, embodiments may be implemented as computer-executableinstructions stored in one or more tangible computer storage media. Aswill be appreciated by a person of ordinary skill in the art, suchcomputer-executable instructions stored in tangible computer storagemedia define specific functions to be performed by computer hardwaresuch as computer processors. In general, in such an implementation, thecomputer-executable instructions are loaded into memory accessible by atleast one computer processor. The at least one computer processor thenexecutes the instructions, causing computer hardware to perform thespecific functions defined by the computer-executable instructions. Aswill be appreciated by a person of ordinary skill in the art, computerexecution of computer-executable instructions is equivalent to theperformance of the same functions by electronic hardware that includeshardware circuits that are hardwired to perform the specific functions.As such, while embodiments illustrated herein are typically implementedas some combination of computer hardware and computer-executableinstructions, the embodiments illustrated herein could also beimplemented as one or more electronic circuits hardwired to perform thespecific functions illustrated herein.

The various systems, devices and/or related methods disclosed herein canbe used to at least partially ablate and/or otherwise ablate, heat orotherwise thermally treat one or more portions of a subject's anatomy,including without limitation, cardiac tissue (e.g., myocardium, atrialtissue, ventricular tissue, valves, etc.), a bodily lumen (e.g., vein,artery, airway, esophagus or other digestive tract lumen, urethra and/orother urinary tract vessels or lumens, other lumens, etc.), sphincters,other organs, tumors and/or other growths, nerve tissue and/or any otherportion of the anatomy. The selective ablation and/or other heating ofsuch anatomical locations can be used to treat one or more diseases orconditions, including, for example, atrial fibrillation, mitral valveregurgitation, other cardiac diseases, asthma, chronic obstructivepulmonary disease (COPD), other pulmonary or respiratory diseases,including benign or cancerous lung nodules, hypertension, heart failure,denervation, renal failure, obesity, diabetes, gastroesophageal refluxdisease (GERD), other gastroenterological disorders, other nerve-relateddisease, tumors or other growths, pain and/or any other disease,condition or ailment.

In any of the embodiments disclosed herein, one or more components,including a processor, computer-readable medium or other memory,controllers (for example, dials, switches, knobs, etc.), displays (forexample, temperature displays, timers, etc.) and/or the like areincorporated into and/or coupled with (for example, reversibly orirreversibly) one or more modules of the generator, the irrigationsystem (for example, irrigant pump, reservoir, etc.) and/or any otherportion of an ablation or other modulation system.

Although several embodiments and examples are disclosed herein, thepresent application extends beyond the specifically disclosedembodiments to other alternative embodiments and/or uses of theinventions and modifications and equivalents thereof. It is alsocontemplated that various combinations or subcombinations of thespecific features and aspects of the embodiments may be made and stillfall within the scope of the inventions. Accordingly, it should beunderstood that various features and aspects of the disclosedembodiments can be combine with or substituted for one another in orderto form varying modes of the disclosed inventions. Thus, it is intendedthat the scope of the present inventions herein disclosed should not belimited by the particular disclosed embodiments described above, butshould be determined only by a fair reading of the claims that follow.

While the embodiments disclosed herein are susceptible to variousmodifications, and alternative forms, specific examples thereof havebeen shown in the drawings and are herein described in detail. It shouldbe understood, however, that the inventions are not to be limited to theparticular forms or methods disclosed, but, to the contrary, theinventions are to cover all modifications, equivalents, and alternativesfalling within the spirit and scope of the various embodiments describedand the appended claims. Any methods disclosed herein need not beperformed in the order recited. The methods disclosed herein includecertain actions taken by a practitioner; however, they can also includeany third-party instruction of those actions, either expressly or byimplication. For example, actions such as “advancing a catheter” or“delivering energy to an ablation member” include “instructing advancinga catheter” or “instructing delivering energy to an ablation member,”respectively. The ranges disclosed herein also encompass any and alloverlap, sub-ranges, and combinations thereof. Language such as “up to,”“at least,” “greater than,” “less than,” “between,” and the likeincludes the number recited. Numbers preceded by a term such as “about”or “approximately” include the recited numbers. For example, “about 10mm” includes “10 mm.” Terms or phrases preceded by a term such as“substantially” include the recited term or phrase. For example,“substantially parallel” includes “parallel.”

What is claimed is:
 1. A method of heat removal from an electrodeassembly during a tissue treatment procedure, the method comprising:delivering energy to an electrode assembly of an ablation system, theablation system comprising a catheter comprising a distal end, theelectrode assembly positioned along the distal end of the catheter; thecatheter of the ablation system comprises a plurality of thermal shuntmembers along its distal end, a first one of the plurality of thermalshunt members extends at least partially through an interior of theelectrode assembly; a second one of the plurality of thermal shuntmembers being disposed proximal to the first one of the plurality ofthermal shunt members, a third one of the plurality of shunt membersbeing distal to and spaced apart from the second one of the plurality ofshunt members by at least a portion of the electrode assembly, thesecond one and the first one of the plurality of thermal shunt membersbeing differently sized; the catheter further comprises at least onefluid passage extending at least partially through the interior of theelectrode assembly and an interior of the plurality of thermal shuntmembers; delivering a fluid through the at least one fluid passage; andtransferring heat from the electrode assembly to the fluid via theplurality of thermal shunt members to reduce the likelihood of localizedhot spots along the distal end of the catheter.
 2. The method of claim1, wherein the plurality of thermal shunt members is configured totransfer heat while not retaining heat, and wherein the plurality ofthermal shunt members comprises a thermal diffusivity greater than 1.5cm²/sec; wherein the electrode assembly comprises at least oneradiofrequency electrode; and wherein the at least one fluid passage isconfigured to place the electrode assembly in fluid communication with afluid source to selectively remove heat from the electrode assemblyand/or tissue of a subject located adjacent the electrode assembly. 3.The method of claim 1, wherein the plurality of thermal shunt members isconfigured to transfer heat while not retaining heat, and wherein theplurality of thermal shunt members comprises a thermal diffusivitygreater than 1.5 cm²/sec.
 4. The method of claim 1, wherein theplurality of thermal shunt members comprises a diamond or othercarbon-based material.
 5. The method of claim 1, wherein the electrodeassembly comprises a composite electrode, the composite electrodecomprising a first electrode portion and at least a second electrodeportion, wherein an electrically insulating gap is located between thefirst electrode portion and the at least a second electrode portion tofacilitate high-resolution mapping along a targeted anatomical area. 6.The method of claim 1, wherein the at least one fluid passage isconfigured to place the electrode assembly in fluid communication with afluid source to selectively remove heat from the electrode assembly andtissue of a subject located adjacent the electrode assembly.
 7. Themethod of claim 1, wherein the at least one fluid passage is in directthermal communication with plurality of thermal shunt members.
 8. Themethod of claim 1, wherein the at least one fluid passage comprises atleast one opening, wherein the at least one opening allows fluid flowingthrough the at least one fluid passage to exit the catheter.
 9. A methodof heat removal from an electrode assembly during a tissue treatmentprocedure, comprising: delivering energy to an electrode assembly of anablation system, the electrode assembly positioned along a distal end ofan elongate body; a plurality of thermal shunt members extends at leastpartially through an interior of the electrode assembly, the pluralityof thermal shunt members further includes a first thermal shunt memberspaced from a second thermal shunt member, the second thermal shuntmember being differently sized that the first thermal shunt member; athird one of the plurality of shunt members being distal to and spacedapart from the second one of the plurality of shunt members by at leasta portion of the electrode assembly; and the elongate body furthercomprises at least one fluid passage extending at least partiallythrough the interior of the plurality of thermal shunt membersdelivering a fluid through the at least one fluid passage; andtransferring heat from the electrode assembly to the fluid via theplurality of thermal shunt members to reduce the likelihood of localizedhot spots along the distal end of the elongate body.
 10. The method ofclaim 9, wherein the at least one thermal shunt member is configured totransfer heat while not retaining heat, and wherein the at least onethermal shunt member comprises a thermal diffusivity greater than 1.5cm²/sec; and wherein the at least one fluid passage is configured toplace the electrode assembly in fluid communication with a fluid sourceto selectively remove heat from the electrode assembly and/or tissue ofa subject located adjacent the electrode assembly.
 11. The method ofclaim 9, wherein the plurality of thermal shunt members is configured totransfer heat while not retaining heat, and wherein the at least onethermal shunt member comprises a thermal diffusivity greater than 1.5cm²/sec.
 12. The method of claim 9, wherein the plurality of thermalshunt members comprises a diamond or other carbon-based material. 13.The method of claim 9, wherein the electrode assembly comprises acomposite electrode, the composite electrode comprising a firstelectrode portion and at least a second electrode portion, wherein anelectrically insulating gap is located between the first electrodeportion and the at least a second electrode portion to facilitatehigh-resolution mapping along a targeted anatomical area.
 14. The methodof claim 9, wherein the at least one fluid passage is in direct thermalcommunication with the plurality of thermal shunt members.
 15. A methodof heat removal from an ablation member during a tissue treatmentprocedure, comprising: delivering energy to an ablation member of anablation system, the ablation member positioned along a distal end of anelongate body; a plurality of thermal shunt members extends at leastpartially through an interior of the ablation member; and at least onefluid passage extends at least partially through an interior of theplurality of thermal shunt members, the plurality of thermal shuntmembers further includes a first thermal shunt member spaced from asecond thermal shunt member, at least a portion of the ablation memberbeing disposed between the first and second thermal shunt members, thesecond thermal shunt member being differently sized that the firstthermal shunt member, a third one of the plurality of thermal shuntmembers being differently sized than first thermal shunt member and thesecond thermal shunt member; delivering a fluid through the at least onefluid passage; and transferring heat from the electrode assembly to thefluid via the plurality of thermal shunt members.
 16. The method ofclaim 15, wherein the plurality of thermal shunt members is configuredto transfer heat while not retaining heat, and wherein the plurality ofthermal shunt members comprises a thermal diffusivity greater than 1.5cm²/sec; and wherein the at least one fluid passage is configured toplace the ablation member in fluid communication with a fluid source toselectively remove heat from the ablation member and tissue of a subjectlocated adjacent the ablation member.
 17. The method of claim 15,wherein the plurality of thermal shunt members is configured to transferheat while not retaining heat, and wherein plurality of thermal shuntmembers comprises a thermal diffusivity greater than 1.5 cm²/sec. 18.The method of claim 15, wherein the plurality of thermal shunt memberscomprises a diamond or other carbon-based material.
 19. The method ofclaim 15, wherein the ablation member comprises a composite electrode,the composite electrode comprising a first electrode portion and atleast a second electrode portion, wherein an electrically insulating gapis located between the first electrode portion and the at least a secondelectrode portion to facilitate high-resolution mapping along a targetedanatomical area.
 20. The method of claim 15, wherein the at least onefluid passage is in direct thermal communication with the plurality ofthermal shunt members.